Preheat oven to 350°F (177°C).

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 attachment, beat the butter and sugar together on high speed until smooth and creamy, about 3 minutes.

Scrape down the sides and bottom of the bowl with a silicone spatula as needed.

Add the eggs and mix on medium speed until combined.

Scrape down the bowl again, and then beat in the sour cream and vanilla extract.

Add about ⅓ of the dry ingredients and ⅓ of the buttermilk, then beat on low speed until combined.

Add another ⅓ of the dry ingredients and ⅓ of the buttermilk, then beat again on low speed until combined.

Add the remaining of each, and beat just until incorporated. Do not over-mix this batter.

There will be around 8 cups of batter total. Divide it in half and transfer half of the batter into another bowl.

Whisk espresso powder into the warmed milk and then add it to one of the batters, along with the cocoa powder and sugar. Whisk until combined; a few small lumps are OK.

Grease three 9-inch round cake pans, line with parchment paper rounds, then grease the parchment paper.

Drop a large spoonful of 1 batter in the center of each pan. Top each circle with a spoonful of the other batter.

Alternate spoonfuls of the batters on top of each other in each pan and repeat until all the batter is used.

Bake for 25–27 minutes, or until the cakes are baked through.

Allow the cakes to cool in the pans set on a cooling rack for 1 hour, then remove them from the pans and let the cakes finish cooling directly on the rack.

In a large bowl using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the cream cheese on high speed until completely smooth and creamy, about 1 minute.

Add the butter and beat until combined.

Add the confectioners’ sugar, cocoa powder, vanilla extract, 1 Tablespoon milk, and salt and beat on low speed; gradually increase the speed to medium-high and beat until combined and creamy.

Assemble the cake by slicing a thin layer off the tops of the cakes to create a flat surface.

Place 1 cake layer on your cake stand, cover the top with about 1 cup of frosting.

Top with the 2nd cake layer, upside down, and cover the top with frosting.

Top with the 3rd cake layer and spread the remaining frosting all over the top and around the sides.

Garnish with sprinkles, if desired. Refrigerate for at least 45 minutes before slicing.