Preheat the oven to 350°F (180°C) and spray two 8-inch cake pans with non-stick spray and line the bottoms with circles of parchment paper. Set aside.
Sift all purpose flour into a mixing bowl and add white granulated sugar, baking soda, salt and cocoa powder. Mix together.
If you're making homemade buttermilk then add 1 and ½ Tbsp lemon juice to a measuring jug and add room temperature milk up to the 1 and ½ cup line. Let it sit for a few minutes to curdle.
Add the buttermilk, vanilla extract, oil, vinegar and red gel food coloring to the mixing bowl and mix into a thick batter. Don't overmix.
Divide the batter evenly between the two prepared 8-inch cake pans and smooth down.
Bake for 30 minutes or until a toothpick inserted into the center of one of the cakes comes out clean.
Let the cakes cool in the pans for a few minutes before removing them from the pans and transferring to a wire cooling rack to cool completely before frosting.