Key Lime Pie Cake

A Key Lime Pie cake that is bursting with lime flavor! The moist key lime cake is baked on a buttery graham cracker crust. In between the layers is a zesty lime curd, and the cake is covered in a smooth vanilla bean buttercream! 

Whether you want a traditional Key Lime Pie or Crumbl Key Lime Pie Cookies, the truth of the matter is that lime is such a fun dessert flavor! 

Why This Recipe Works

• Prominent key lime flavor. The key lime cake from scratch uses key lime juice and the zest in the curd and the cake layers. This enhances the flavor so much more than just using the juice!  
• Key lime pie in cake form. Baking the lime cake on a graham cracker crust helps mimic the key lime pie even more! Plus, it provides a nice bit of texture difference in this key lime cake recipe.
• Vanilla bean paste provides flavor and flair. Using vanilla bean paste provides a more prominent vanilla flavor. Instead of the vanilla being in the background, is it the star of the show! The flecks also provide a fancy flair to the look of the vanilla bean buttercream. 

Ingredient Notes

• Graham Cracker Crumbs: You’ll want the graham crackers to be very fine so you get a smooth texture in the crust. 
• Unsalted Butter: You’ll need butter for the crust, the curd and the buttercream. Pay attention to the details in the recipe card for which element requires melted, soft, or cold butter. 
• Cake Flour: Cake flour is a finer consistency than regular all-purpose flour. While you can make your own, I find it’s easier to buy. I like the Softasilk brand. 
• Oil: You’re welcome to use a neutral flavored oil (grapeseed, vegetable oil, canola, etc.). Using oil in the cake is what provides a very moist cake texture. 
• Buttermilk: Be sure to use room temperature wet ingredients when making cake. This helps the wet ingredients incorporate into the cake batter more nicely, helping the bake. 
• Sour Cream: Yes, even the sour cream should be room temperature. I used full-fat sour cream because the sour cream provides not just a tart, tangy flavor, but additional fat to keep the cake moist. 
• Key Lime Juice: For the curd, use store bought key lime juice. I tried using freshly squeezed key lime juice and the curd would always come out bitter. But the store bought juice was always perfect! I prefer the Nellie and Joe’s brand. If you want to use freshly squeezed for the cake, that is fine. 
• Vanilla Extract: Note that you’ll use vanilla bean paste in addition to vanilla extract in this cake recipe. 
• Key Lime Zest: You can use zest of limes if you can’t find key limes. Key limes have a much punchier lime flavor than regular limes. 
• Powdered Sugar: Sifting the powdered sugar will ensure a smooth buttercream texture. 
• Vanilla Bean Paste: Vanilla bean paste is a bit thicker than extract. It has a richer vanilla flavor and includes the vanilla bean flecks, which provides a nice visual for the cake. 

Step-by-Step Instructions

1. Make the graham cracker crust. Add the graham cracker crumbs, melted butter, sugar, and salt to a large bowl. Mix until combined. Spray three 8-inch round cake pans with nonstick cooking spray. Line the bottoms with parchment paper and spray the parchment paper too. Press 1/3 of the mixture into the bottom of each cake pan. Bake at 325° F for 4 minutes. Remove and let cool while making the key lime pie cake layers. 
2. Make the key lime pie cake batter. Whisk the cake flour, baking powder, and salt in a medium bowl and set aside. Combine the sour cream, buttermilk, lime juice, lime zest, and vanilla in a smaller bowl. Beat the sugar and oil for 2-3 minutes in the bowl of a stand mixer until light in color and well combined. Add the eggs, one at a time, beating well after each addition. 
3. Combine the wet and dry ingredients. With the mixer on low speed, add 1/3 of the flour mixture, followed by ½ of the buttermilk/sour cream mixture, mixing after each addition until all combined, ending with the flour.  Do not over mix! Divide the batter evenly among the cake pans, pouring directly on top of the graham cracker crusts. 
4. Bake the lime cake. Bake at 325°F for 28-34 minutes or until a toothpick inserted into the center comes out with a few moist crumbs. Remove from the oven and let cool in the pans for about 15 minutes. Turn out onto a wire rack to cool completely. 

5. Make the lime curd. Combine the egg yolks, eggs, and sugar to a saucepan. Cook on medium-low heat until thickened. Add the lime juice and set and cook for a few more minutes until the mixture can coat the back of a spoon. Remove from heat and add the butter, one tablespoon at a time, mixing until all melted and incorporated. If you’d like your curd to be a bit more green, add a couple of drops of food coloring. Pour through a strainer while still hot to remove chunks. Cover and chill in the fridge until completely cool. 
6. Make the vanilla bean buttercream. Beat the butter in the bowl of a stand mixer with the paddle attachment until light in color and smooth in texture. Add the vanilla bean paste and salt and mix until combined. Slowly add the powdered sugar, one cup at a time, mixing after each addition. Add the cream as needed for consistency. Once all the ingredients have been mixed in, beat on high for 3 minutes. 

7. Assemble and crumb coat. Place a cake layer with crust side up on a cake board or stand that has a small dollop of buttercream. Spread a thin layer of buttercream evenly over the top of the graham cracker crust. Pipe a rim of buttercream around the top edge to create a dam. Add 1/2-2/3 cup lime curd inside the buttercream dam. Repeat steps 2 and 3 with the second layer of cake, graham cracker side up. Place the third cake layer on top, graham cracker side up, and crumb coat the entire cake in a thin layer of buttercream. Flash freeze for 5-10 minutes or until the buttercream is cold and no longer soft. 

8. Frost and decorate the cake. Remove the key lime pie cake from the freezer and finish frosting the entire cake. You can add additional decorating, if desired, by piping swirls on the top and topping with lime slices and adding crushed graham crackers along the sides of the cake. We made 1/4 more of the frosting for the swirls. 

Recipe Tips

Putting a small bit of buttercream on the cake board or stand will keep the cake from sliding around as you assemble it.

Be sure to not overfill the cake with lime curd as it will seep out when you add the next layer. This will make the cake unstable and difficult to finish assembling.

If you would like your lime curd to be a little more green, add some food coloring.

We made an extra 1/4 batch of buttercream to make the swirls around the top of the cake. If you want to do any decorating with frosting, I would recommend making 1/4 more of the buttercream. 

When combining the wet ingredients with the dry ingredients, do not over mix! Over mixing cake batter at this stage will result in a tough batter which can affect the rise of the cakes. You want to mix the wet with the dry until just combined. Feel free to really well mix the wet ingredients or the dry ingredients in their separate bowls, but once you combine them, do not over mix! 

Putting the crust side up means the crust won’t be directly on top of the lime curd, which could soak up some of the moisture from the curd and get soggy. Putting the lime cake layer upside down makes it so the layer of buttercream is a barrier between the crust and the curd.

Make Ahead, Storing, and Freezing

If making ahead of time, remove the cake layers from the pans and wrap with plastic wrap and store in the freezer for up to 3 weeks.

The lime curd can be made ahead of time and stored in the fridge for up to 4 days.

If making the buttercream ahead of time, store in an airtight container in the fridge or freezer. Let come to room temperature and beat until light and fluffy. 

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

Recipe FAQs

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