Preheat the oven to 350°F. Grease and flour two 9-inch round cake pans or line the bottoms with parchment paper.
In a large mixing bowl, beat the butter and granulated sugar until light and fluffy, about 3 to 5 minutes.
1 cup butter, softened, 1½ cups granulated sugar
Beat in the vanilla extract.
1 teaspoon vanilla extract
Add the eggs, one at a time, beating well after each addition.
3 large eggs
In a separate bowl, whisk together the cake flour, cocoa powder, baking powder, and salt.
3 cups cake flour, 2 tablespoons cocoa powder, 1 tablespoon baking powder, ½ teaspoon salt
Add the dry ingredients to the butter mixture in three additions, alternating with the chocolate milk. Begin and end with the dry ingredients. Mix just until combined after each addition.
1 cup chocolate milk
Divide the batter evenly between the prepared cake pans and smooth the tops.
Bake for about 30 minutes, or until a toothpick inserted into the center comes out clean.
Cool the cakes in the pans for 10 minutes, then turn them out onto wire racks to cool completely before frosting.
Make the frosting
Beat the softened butter until smooth and creamy.
⅔ cup butter
Gradually beat in the powdered sugar and cocoa powder.
5⅓ cups powdered sugar, 1⅓ cups cocoa powder
Add the chocolate milk and vanilla extract.
⅔ cup chocolate milk, 2 teaspoons vanilla extract
Beat until the frosting is light, fluffy, and spreadable. If needed, add a splash of additional chocolate milk to thin the frosting or a little more powdered sugar to thicken it.
Assemble the cake
Place one cooled cake layer on a serving plate.
Spread an even layer of frosting over the top.
Add the second cake layer.
Frost the top and sides of the cake.
Slice and serve.
Notes
🥡 Storage
Store the frosted cake covered at room temperature for up to 2 days.
Refrigerate for up to 5 days.
Allow refrigerated slices to come to room temperature before serving for the best texture.
♨️ Reheating
This cake is best served at room temperature and does not require reheating.
If desired, microwave an individual slice for 8 to 10 seconds for an extra soft texture.
❄️ Freezing
Freeze unfrosted cake layers tightly wrapped for up to 3 months.
Freeze individual frosted slices in airtight containers for easy desserts.
Thaw overnight in the refrigerator, then bring to room temperature before serving.
💡 Tips for Best Results
Use room temperature butter, eggs, and chocolate milk.
Measure cake flour using the spoon-and-level method.
Do not overmix after adding the flour.
Bake just until a toothpick comes out clean.
Cool the cake completely before frosting.
Chill the frosted cake for 20 minutes before slicing for cleaner cuts.
🍳 Alternate Cooking Methods
Bake in a greased 9x13-inch baking pan for a sheet cake. Increase or decrease the baking time as needed until a toothpick comes out clean.
Divide the batter into cupcake liners, filling each about two-thirds full, and bake until a toothpick inserted into the center comes out clean.
♻️ Leftovers
Cube leftover cake for parfaits, then layer with whipped cream.
Turn slices into cake pops.
Crumble over vanilla ice cream.
Use leftovers in a chocolate trifle.
📝 Notes
Cake flour gives the softest texture, but all-purpose flour may be substituted if needed.
Chocolate milk adds moisture and enhances the chocolate flavor without making the cake overly rich.
For the smoothest frosting, sift the cocoa powder and powdered sugar before mixing.
This cake is even better the next day, after the flavors have had time to develop.