1. Preheat the oven to 350 degrees. Grease and flour two 9-x-2-inch cake pans or line their bot- toms with greased, floured waxed paper.
2. Sift the flour, salt, baking powder, and baking soda together twice. In a small mixing bowl, whisk the cocoa, red food coloring, and water to a smooth paste, about 1 minute, and reserve.
3. In a large mixing bowl, beat 1 cup butter with an electric mixer until creamy, about 30 sec- onds. Add the sugar, G cup at a time, beating about 15 seconds after each addition and scraping down the sides of the bowl if necessary, until the mixture has lightened in color and become fluffy, about 2 minutes. Add eggs, 1 at a time, the vanilla, and orange zest, beating for 15 seconds after each addition. Add the red cocoa paste and mix until evenly incorporated.
4. Add the flour mixture to the butter and egg mixture in thirds, alternating with 2 additions of half the buttermilk. To avoid overworking the batter, gently mix with a wooden spoon or rubber spatula after each addition, until the ingredient is just incorporated. Once all ingredients are incorporated, beat the batter 10 to 12 strokes with your spoon or spatula if using cake flour, 2 to 3 strokes if using bleached all-purpose flour.
5. Divide the batter between the cake pans and spread the tops evenly with the wooden spoon or spatula. Bake until a cake tester or toothpick emerges clean, about 30 minutes. Remove from the oven and let the cakes cool in their pans on a rack for 10 minutes, then slide a thin paring knife around the edge of the pans and invert the cakes. Lift away the waxed paper, if using. Cool the cakes completely on a rack, with their tops facing up.
6. In a large bowl, beat I cup butter with the mixer until creamy, about 30 seconds. Add the cream cheese and beat until the mixture is fluffy, white, and very smooth, about 1 minute. Add the confectioners’ sugar 1 cup at a time, beating for 30 seconds after each addition, until the mixture is creamy, fluffy, and smooth. If the frosting is too stiff, beat the milk into it to loosen it.
7. Gently ice the cake layers generously. Spoon 1 cup of icing in the center of the first cake layer. Working an icing or rubber spatula in gentle swirling motions, spread the icing from the center toward the edges of the cake until it forms an even layer (if you need to add more icing, add it to the center and work it out toward the sides).
8. Carefully set the second cake layer on top of the first and ice the second layer in the same manner, beginning with a dollop in the center and working it out to the sides. Then ice the sides of the cake. (If you prepared your pans well, the sides of the cake should have pulled away from the pan and baked to a firm, flat surface. But if the sides are crumbly, brush excess crumbs away and place a thin layer of icing on the cake to seal the crumbs in. Refrigerate for 30 minutes, then apply another, thicker layer on top of the first.)
9. Store the cake at room temperature, beneath a cake cover. If you don’t plan to eat it for 24 hours, put it on a plate, tent it with plastic wrap, and store it in the refrigerator for up to 3 days. Remember to remove the cake from the refrigerator 1 hour or more before serving to take the chill off. Serve with glasses of cold milk.