Preheat the oven to 350°F. Butter and flour three 9-inch round cake pans.
In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
3¾ cups Cake Flour, 1½ teaspoons baking soda, 1½ teaspoons Kosher salt
In a large bowl or stand mixer fitted with the paddle attachment, beat the butter on medium speed until smooth. Add the sugar and beat until light and fluffy, about 3 minutes.
¾ cup salted butter, 2¼ cups granulated sugar
Add the eggs one at a time, mixing well after each addition. Beat in the vanilla extract.
3 large eggs, 3 teaspoons vanilla extract
Sift the cocoa powder into the bowl and mix just until combined, scraping down the sides as needed.
3 tablespoons unsweetened cocoa powder
In a liquid measuring cup, stir together the buttermilk, vinegar, and red food coloring.
1½ cups buttermilk, 1½ tablespoons white vinegar, 1½ –2½ tablespoons gel red food coloring
With the mixer on low speed, add half of the flour mixture, followed by half of the buttermilk mixture, mixing just until combined. Repeat with the remaining flour mixture and buttermilk mixture.
Divide the batter evenly among the prepared pans.
Bake for 30–35 minutes, or until the centers spring back lightly when touched and a toothpick inserted comes out clean.
Cool the cakes in the pans for 10 minutes, then turn out onto wire racks and cool completely before frosting.