Combine flour, salt, and cocoa powder in a medium bowl. Set aside.
Preheat oven to 350℉/177℃. Grease three 9-inch round baking pans with baking spray, then line them with parchment paper (if desired) and set aside.
Cream the butter and sugar on high in a stand mixer until fluffy and starts looking white (approximately 4 minutes).
Add sour cream and continue mixing for another minute. Follow with the oil, and mix a minute longer. Add the eggs one at a time, beating the mixture well between each addition.
Next, pour in the buttermilk, vinegar, and vanilla and thoroughly mix.
Add food coloring until you reach the desired color.
Add the flour mixture slowly to the wet ingredients. Then mix the baking soda and powder with the water and gently fold it into the cake batter. Scrape the sides of your mixing bowl down as you go.
Evenly divide your batter between the three pans, and tap on the countertop to release bubbles.
Bake at 350℉/177℃ for 25-30 minutes (check for doneness by inserting a knife or toothpick in the cake's center. If it comes out clean, it's done).
Let the cake layers sit in their pans for 10-15 minutes. Gently invert them on a wire rack and lift off the pans. Once the layers have cooled completely, wrap them in cling wrap and chill them in the refrigerator for an hour (preferably overnight) because it makes them much easier to frost.
Let the cake layers sit in their pans for 10-15 minutes. Gently invert them on a wire rack and lift off the pans. Once the layers have cooled completely, wrap them in cling wrap and chill them in the refrigerator for an hour (preferably overnight) because it makes them much easier to frost.