This Lemon Poppy Seed Cake with Cake Mix is a deliciously moist doctored cake made with a lemon cake mix, sour cream, buttermilk and lemon zest! This lemon poppy seed layer cake is filled and frosted with a silky smooth lemon-infused vanilla buttercream that is the perfect complement to the cake! 

I’m a total sucker for lemon poppy seed desserts! My Lemon Poppy Seed Bundt Cake is another delicious lemon poppy seed cake recipe from scratch in a bundt pan! Prefer something smaller? Make my Lemon Poppy Seed Muffins with Sour Cream, Lemon Poppy Seed Cookies with Lemon Curd or my Lemon Poppy Seed Scones! Round out your lemon poppy seed dessert recipes with my Easy Lemon Poppy Seed Bread. Told you I’m a big fan! 

A slice of Lemon Poppy Seed Cake made with Cake Mix on a plate with three pink flowers near the cake.

Why This Recipe Works

  • Uses a lemon cake mix. Making this lemon poppy seed with cake mix is a great way to cut on the prep time. Instead of mixing lots of dry ingredients together, just use the box mix for an easy poppy seed cake! This is a doctored cake, so we’ll be adding more wet ingredients to really make it taste amazing!
  • Moist lemon cake. Thanks to using sour cream, buttermilk, and vegetable oil, this cake is incredibly moist! Forget the dry box cakes! When you make this recipe, you’ll get the simplicity of the cake mix with the delicious flavors and moistness of a cake from scratch! Truth be told, this cake was devoured within 24 hours of making it!
  • Lots of lemon zest. Using lemon zest in the cake and in the frosting is the best way to get a prominent lemon flavor! 

Ingredient Notes

A Lemon Poppy Seed Cake with Cake Mix layered cake on a wooden cake stand covered in a white buttercream frosting.
  • Duncan Hines Lemon Supreme Cake Mix: I’ve seen many a lemon poppy seed cake recipe using cake mix from a yellow cake mix box. I wanted to use a lemon cake mix to really lean into the lemon flavor more. Feel free to use whatever brand. 
  • Vegetable Oil: Cakes made with vegetable oil will be much more moist since oil is a liquid at room temperature. 
  • Sour Cream: Making a lemon poppy seed cake with cake mix and sour cream is the best way to get a really moist lemon poppy seed cake. The extra fat (and flavor) makes a huge difference!
  • Buttermilk: Be sure to pull out the buttermilk at least 30 minutes before making the cake so it comes to room temperature. This will help it incorporate into the cake better, giving you a much more even bake. 
  • Fresh Lemon Zest: You’ll need about 3-4 lemons. There isn’t much lemon flavor in the cake mix alone, so this recipe uses fresh lemon zest in the cake and in the frosting. This really amps up the lemon flavor throughout the lemon poppy seed cake mix. 
  • Unsalted Butter: For the frosting, you’ll want the butter to be cool but not cold. It should be colder than room temperature. 
  • Powdered Sugar: Be sure to sift the powdered sugar for the smoothest buttercream texture. 
  • Heavy Cream: Don’t add the cream all at once. Do it little by little so that you can get your desired consistency.

Step-by-Step Instructions

  1. Combine the cake mix and poppy seeds. Add the lemon cake mix and poppy seeds to a medium bowl and whisk until combined. Set aside. 
A white bowl with dry ingredients and poppyseeds in it for making Lemon Poppy Seed Cake with Cake Mix.
  1. Combine the wet ingredients. In a large bowl (or bowl of a stand mixer fitted with the paddle attachment), add the eggs, vegetable oil, buttermilk, sour cream, vanilla and lemon zest. Mix until well combined. 
A glass mixing bowl with eggs, vanilla, sour cream, and lemon zest in it.
  1. Add dry ingredients to the wet. Add the cake mix and poppy seed mixture into the bowl with the wet ingredients. Using a spatula or on low speed, gently mix until just combined. Do not over mix! 
  2. Bake. Divide the lemon poppy seed cake batter evenly among three 6-inch round cake pans (that have been sprayed with nonstick cooking spray, lined with a parchment paper circle on the bottom and sprayed again). Bake at 325ºF for 31-34 minutes or until a toothpick in the center comes out with a few moist crumbs. 
  3. Let cool. Remove the pans from the oven and let cool in the pans for 5-10 minutes before turning out onto a wire rack to cool completely.
  4. Make the lemon poppy seed cake frosting. In the bowl of a stand mixer fitted with the battle attachment, cream the butter until smooth and light in color. Add the powdered sugar (one cup at a time), adding heavy cream (or milk) 1 tablespoon at a time to keep the consistency beatable. Add the vanilla. Once all the ingredients have been added, beat the buttercream for 2-3 minutes on medium speed or until light in color and fluffy in texture. 
Three six inch round cake pans filled with lemon poppy seed cake batter.

Recipe Tips

You do not want to over mix the batter once you combine the wet and dry ingredients. Over mixing cake batter is one cause of cakes sinking in the oven. Feel free to mix the wet ingredients really well (this is what we want!) but once you add the dry ingredients, gently stir until everything is just barely combined. 

You can make this in two 8-inch round cake pans if you’d like. The bake time will be different (only 25-27 minutes).

Use a kitchen scale to ensure even amounts of batter are in each pan. I like to use a small offset spatula to even the batter along the top.

Make sure your oven rack is placed on the middle rack or the rack above the middle slot.

To test for a cake’s doneness insert a toothpick into the center of the cake, if the toothpick comes out clean, the cake is done. You can also touch the top of the cake and it should spring back slightly.

If the frosting is too thick, add more heavy cream or milk. If the frostings consistency is too thin, add more powdered sugar. 

If you want additional frosting to pipe any decorations on the cake, be sure to 1.5 the recipe. 

Climate plays a big role in baking so keep that in mind in terms of your bake time. 

Make Ahead, Storing, and Freezing

Store any leftover buttercream in an airtight container in the fridge for 7 days or in the freezer for 1-2 months. Remove and let thaw in the fridge and then let come to room temperature. Return to a mixing bowl and beat until fluffy. 

Store the cake covered in the fridge (due to the heavy cream in the frosting) for 4-5 days.

For information on storing and freezing cakes, check out my How to Store and Freeze Cakes guide!

A slice of lemon poppy seed layered cake made from a cake mix on a plate that's resting on a gray napkin.

Recipe FAQs

What can you add to a box cake mix to make it taste better?

There are a few things I love to add to a cake mix to pimp a cake. These include buttermilk, sour cream, and added flavoring (this can include extracts, zests, etc). A doctored cake mix with sour cream is a great way to pimp a cake to make it more flavorful and more moist! 

What is a doctored cake?

A doctored cake (also referred to as a doctored cake mix) is when you take a store-bought box cake mix and add additional ingredients (that aren’t listed on the box) to the cake for added texture, flavor, and moistness. This lemon poppy seed cake with cake mix is a doctored cake because we use cake mix plus other wet ingredients to enhance the cake. 

How do you make a semi-naked cake?

If you aren’t fond of frosting, no worries! I understand. To make this a naked lemon cake, half the frosting recipe. When frosting the cake, rather than having a thick layer of frosting between each cake layer, do a smaller amount. Then do a thin crumb coat on the exterior of the cake.

Do I need fresh lemons for this recipe?

Yes you do! The whole point of making a doctored cake mix is to really amp up the box cake so it tastes like a bakery cake! For this reason, we need fresh ingredients and bright flavors. Using fresh lemon zest will really give a strong and prominent lemon flavor to the cake that you just don’t get with the lemon cake mix on its own. 

A fork cutting into a slice of lemon poppy seed layer cake on a tan plate.

More Lemon Desserts

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A slice of lemon poppy seed layer cake on a tan plate.
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5 from 4 votes

Lemon Poppy Seed Cake with Cake Mix

This moist lemon poppy seed layer cake is made with a lemon cake mix, sour cream, buttermilk and fresh lemon zest! This cake is perfect for brunch, parties, birthdays, or just weeknight eating.
Prep Time: 35 mins
Cook Time: 35 mins
Total Time: 1 hr 10 mins
Servings: 10 servings

Ingredients
 

  • 1 15.25 oz box Duncan Hines Lemon Supreme Cake mix
  • 2 tablespoons poppy seeds
  • 3 large eggs - at room temperature
  • 1/3 cup vegetable oil
  • 2/3 cup sour cream
  • 3/4 cup buttermilk - at room temperature
  • 2 teaspoons vanilla extract
  • 2 tablespoons lemon zest - zest from about 2-3 lemons

Frosting

  • 3/4 cup unsalted butter - softened
  • 6-7 cups powdered sugar
  • 1/2 teaspoon vanilla extract
  • 1/3 cup heavy cream or milk - don’t add it all at once. Do it little by little so that you can get your desired consistency
  • 1 tablespoon lemon zest

Instructions
 

  • Preheat to 325. Grease and flour 3 – 6 inch round cake pans. Set aside. 
  • In a medium size bowl whisk the cake mix and the poppy seeds. Set aside.
  • In a large bowl combine the eggs, vegetable oil, sour cream, buttermilk, vanilla, and lemon zest. Whisk until everything is thoroughly combined. *
  • Add the cake mix to the wet ingredients. Using a spatula, mix the cake mix until combined. Don’t over mix! Alternatively, you can use a stand mixer (like I did). See recipe notes for details. 
  • Divide the cake batter evenly amongst the cake pans. 
  • Bake for 31-34 minutes or until a toothpick inserted in the center comes out clean; and when the top of the cake is touched it and gently springs back. Mine baked for 33 minutes. All ovens are different, so keep an eye on yours.
  • Cool on a wire rack in the pans for 5-10 minutes, then remove the cakes from the pans and allow to cool completely. 
  • Once cool, frost the cakes. Or, you can double wrap the cakes individually in plastic wrap and refrigerate or freeze.  

Lemon Frosting

  • Cream butter until smooth. Add powdered sugar, vanilla extract, and heavy cream (or milk) one tablespoon at a time. Once reached your desired consistency, whip on medium high speed for 1-2 minutes.

Notes

You can bake this in two 8-inch round cake pans. Bake for 25-27 minutes or until a toothpick inserted in the center comes out clean. 
For information on storing and freezing cakes, check out my How to Store and Freeze Cakes guide!

Nutrition

Calories: 588kcal (29%)Carbohydrates: 74g (25%)Protein: 3g (6%)Fat: 27g (42%)Saturated Fat: 17g (85%)Cholesterol: 109mg (36%)Sodium: 59mg (2%)Potassium: 86mg (2%)Sugar: 72g (80%)Vitamin A: 645IU (13%)Vitamin C: 2.5mg (3%)Calcium: 79mg (8%)Iron: 0.5mg (3%)
Course: Dessert
Cuisine: American
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