• Preheat the oven to 350 F. Spray 3 8-inch round pans (or 2 8-inch or 9-inch cake pans) with cooking spray and line with parchment paper. Set aside.
• Combine the flour, cocoa powder, salt, and baking soda; mix with a whisk to blend and set aside.
• In a mixing bowl with an electric mixer, beat the butter until smooth and creamy. Add the granulated and brown sugars and beat on low speed until well blended.
• Add the eggs and beat until blended.
• Add the vegetable oil, vanilla, vinegar, and food coloring; mix until blended.
• Add 1/3 of the flour mixture and 1/2 of the buttermilk; mix well. Repeat with another 1/3 of the flour mixture and the remaining buttermilk and mix well. Add the remaining flour and beat just until smooth and well blended.
• Divide the batter evenly among the 3 pans (or 2 pans) and spread with a spatula.
• Bake the layers in the preheated oven for 25 to 30 minutes, until the cake bounces back when lightly touched with a finger.
• Cool the cakes in the pans on a rack for about 20 minutes. Remove them from the pan and cool completely on racks before frosting and assembling the layers.

Prepare the Frosting and Assemble the Cake

• In a mixing bowl with an electric mixer, beat the cream cheese until smooth. Add the butter and salt and beat until well combined.
• Add 4 cups of confectioners' sugar and beat on low speed until well blended. Add more confectioners' sugar if a thicker frosting is desired, then beat in the vanilla. Continue to beat for a minute or 2, until smooth and creamy.