Preheat the oven to 350°F (180°C). Spray two 9-inch cake pans* with non-stick spray and line the bottoms with circles of parchment paper.
Sift the all purpose flour into a mixing bowl and add the sugar, baking soda, salt and cocoa powder. Mix together.
If you're making homemade buttermilk then add 1 Tbsp lemon juice to a measuring jug and add room temperature milk up to the 1 cup line. Let it sit for a few minutes to curdle.
Add the buttermilk, eggs, oil, vanilla, vinegar and red food coloring in with the dry ingredients and mix into a batter. Mix until it's just mixed. Use a hand whisk briefly to get rid of any lumps but don't overmix.
Divide the batter evenly between your prepared cake pans.
Bake for 30 minutes or until a toothpick inserted into one of the cakes comes out clean.
Transfer to a wire cooling rack to cool completely before frosting.