Preheat oven to 350°F. Spray a 9x13 inch pan with nonstick cooking spray that contains flour, and set aside.
In the bowl of a stand mixer fitted with a paddle attachment, stir the flour, baking powder, baking soda, salt, cocoa powder, and sugar. Add the butter and oil to the dry ingredients and mix on low speed until the mixture resembles sand.
In a large liquid measuring cup whisk the vanilla, milk, and hot water. Pour into the dry ingredients and butter mixture and mix until combined.
Add the eggs, 1 at a time, mixing after each addition. Once fully combined, pour the batter into the prepared baking pan.
Bake for 28-34 minutes or until a toothpick inserted in the center comes out clean. Remove from the oven and set on a wire rack to cool completely.
Peanut Butter Frosting
Make the frosting: In the bowl of a stand mixer, or using a hand-held electric mixer, beat the butter and peanut butter until creamy and well combined. With the mixer on low, gradually add the powdered sugar, ½ cup at a time until all of the powdered sugar has been added. Scrape down the sides of the bowl as needed.
Mix in the vanilla, salt, and milk. Turn the mixer to medium-high speed and beat for 30 seconds to 1 minute.
Spread the frosting onto the cooled cake.
Top the cake with mini chocolate chips or melted chocolate drizzled overtop, if desired.
Notes
The butter used in the cake needs to be very soft. If you gently poke your finger into the butter and it leaves a dent, it’s ready to use.If using unsweetened cocoa powder, the cake will be much lighter in color and won't have as rich of a chocolate flavor. Read my Best Cocoa Powder for Baking post for more information on the differences of cocoa powders. Store the cake covered at room temperature for 2-3 days.Cake recipe adapted from King Arthur Flour.