Preheat the oven to 350º F. Grease two or three 8 inch springform pans with butter (butter the sides and bottom) and line each pan with a parchment paper circle for easy cake removal. Set aside.

In a small mixing bowl combine the flour, baking powder, baking soda, and salt.

In a large mixing bowl combine the butter and sugar, beat using an electric mixer, 1-2 minutes until fluffy.

Add in the eggs, sour cream, milk, and vanilla extract. Beat with the electric mixer.

Gradually add the flour mixture to the wet ingredients, mixing just until the flour is incorporated.

Add 2 ½ to 2 ¾ cups of batter to a separate mixing bowl, about 610-630 grams of batter. Gently mix the melted chocolate into the batter.

Evenly divide the batter among the pans. I found that the batter looked most marbled when I alternated small dollops of each batter, swirling and repeating until the batter is gone. If using 2 pans, that’s 2 ½ to 3 cups of batter per pan, if using 3 pans, that’s 2 cups of batter per pan. If you have bake even cake strips, secure them around the outside of the pans.

Bake 2 pans for 40-45 minutes or 3 pans for 32-37 minutes or until a toothpick inserted in the center comes out clean.

Allow the cakes to cool for 20-30 minutes in the pans, then use a small spatula to loosen the cake from the edge of the pan. Remove the cake from the pans and allow them to cool completely on a cooling rack.

In a mixing bowl, beat the butter on high for 3 minutes.

Sift in the cocoa powder and 3 cups of powdered sugar. I like to sift these in because it helps break up clumps, creating a light and fluffy frosting. Beat the frosting on low speed until combined and thick.

Mix in 3 tbsp of heavy cream, vanilla extract and salt.

Add in the additional powdered sugar (1-2 cups), mix on low. If the frosting is too thick, beat in an additional tablespoon of heavy cream.

If needed, level the cooled cakes using a cake leveler or serrated knife.

Spread a small amount of frosting on the bottom of your cake plate / stand, this acts as “glue” to prevent the cake from moving. Place one cake layer over the frosting. Measure 3/4 to 1 cup of frosting and evenly spread that on top of the first layer. Top with the second cake layer and spread another ¾ to 1 cup of frosting on top of that layer. Use the remaining frosting around the sides and top of the cake.