Step 1

Preheat oven to 350°F (177°C). Grease three 9-inch round cake pans, line with parchment paper rounds, then grease the parchment paper. Parchment paper helps the cakes seamlessly release from the pans. (If it’s helpful, see this parchment paper rounds for cakes video & post.)

Step 2

Whisk the flour, salt, baking powder, and baking soda together in a large bowl. Set aside. Using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the butter and sugar together on high speed until smooth and creamy, about 3 minutes. Scrape down the sides and up the bottom of the bowl with a silicone spatula as needed. On medium-high speed, add 1 egg at a time, beating well after each addition. Beat in the sour cream and vanilla extract. Scrape down the sides and up the bottom of the bowl with a silicone spatula as needed.

Step 3

With the mixer on low speed, add the dry ingredients in three additions alternating with the buttermilk, beginning and ending with the dry ingredients, and mixing each addition just until incorporated. Do not overmix this batter. The batter will be smooth, velvety, and slightly thick.

Step 4

There will be around 8 cups of batter total. Transfer half of it to another bowl. Whisk in the 4 chocolate batter ingredients until combined. A few small lumps are ok.

Step 5

First, watch the video above to see exactly how to layer the batters into the cake pans. Drop a large spoonful of 1 batter in the center of the pan. Top with a spoonful of the other batter. Alternate spoonfuls on top of each other. Give the pan a shake to level it all out. Repeat with each cake pan until all the batter is used. There’s about 8 cups of batter total, so each cake pan will have a little less than 3 cups of batter in it.

Step 6

Bake for around 25-27 minutes or until the cakes are baked through. To test for doneness, insert a toothpick into the center of the cake. If it comes out clean, it is done. Allow cakes to cool completely in the pans set on a wire rack. The cakes must be completely cool before frosting and assembling.

Step 7

In a large bowl using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the cream cheese for 1 minute on high speed until completely smooth and creamy. Beat in the butter until combined. Add the confectioners’ sugar, cocoa powder, vanilla extract, 1 Tablespoon milk, and salt and beat on medium-high speed until combined and creamy. Add 1 more Tablespoon of milk to slightly thin out, if desired. Taste, then add another pinch of salt if desired.

Step 8

First, using a large serrated knife, slice a thin layer off the tops of the cakes to create a flat surface. Discard (or crumble over ice cream!). Place 1 cake layer on your cake stand, cake turntable, or serving plate. Evenly cover the top with frosting. Top with 2nd layer and evenly cover the top with more frosting. Top with the third cake layer. Spread the frosting into a thick layer all over the top and sides. Garnish with sprinkles, if desired. Refrigerate for at least 45 minutes before slicing. This helps the cake keep its shape when cutting—it could slightly fall apart without time in the fridge.

Step 9

Cover leftover cake tightly and store in the refrigerator for 5 days.