This is adapted from a B. Smith cake on Epicurious
Red Velvet Cake
2 1/4 cups sifted cake flour (sifted, then measured 225 grams weigh)
4 tablespoons natural unsweetened cocoa powder (don’t use Dutch or dark)
1 teaspoon baking powder
1/2 teaspoon salt
1 cup buttermilk
2 generous tablespoons red food coloring (1 oz bottle)
1 teaspoon vanilla extract
1 1/2 cups granulated sugar
8 oz (2 sticks) unsalted butter, cool room temperature
2 large eggs, room temperature
1 teaspoon white vinegar
1 teaspoon baking soda
2 8-ounce packages cream cheese, room temperature
1/2 cup (1 stick) unsalted butter, room temperature
1 tablespoon vanilla extract
2 1/2 cups powdered sugar
Preheat oven to 350 degrees. Spray two 9-inch round pans with flour added cooking spray or rub with shortening and dust with flour.
Sift together cake flour, cocoa, baking powder and salt; set aside.
Mix buttermilk, food coloring, and vanilla in small bowl or large glass measure; set aside.
Beat sugar and butter in large bowl, using an electric mixer, until light and creamy. Add eggs 1 at a time, beating until well blended after each addition. Add 1/3 of the flour mixture and stir until blended. Stir in half of the buttermilk, then another third of the flour mixture. Stir in remaining buttermilk and finally, remaining flour mixture. Stir vigorously until lumps or gone or beat on low speed of mixer.
Mix vinegar and baking soda together in a small cup. It will fizz up. Add fizzy mixture to batter and stir. Working quickly, divide batter between pans and bake cakes on center rack for 25-28 minutes or until a wooden skewer inserted in center comes out clean.
Cool in pans on racks 10 minutes. Turn cakes out onto racks; cool completely.
Beat cream cheese and butter in large bowl until smooth. Beat in vanilla. Add powdered sugar and beat until smooth.