Preheat the oven to 350°F.
Grease and line two 9-inch round cake pans with parchment paper, and then grease the parchment paper and dust with cocoa powder.
Sift the dry ingredients (flour, cocoa, baking powder, baking soda, and salt) into a medium bowl.
In the bowl of a stand mixer, beat the butter for 3 to 5 minutes until soft and light, scraping the bowl intermittently.
Add the sugar and beat until light and fluffy, another 1 to 2 minutes.
Add the eggs, one at a time, and beat for one minute after each addition.
Scrape the bowl, add the vanilla, and beat for an additional minute.
Measure out the buttermilk into a 2-cup measuring cup, then add the vinegar and food coloring.
Add the dry ingredients in three parts, alternating with the buttermilk mixture in two parts, starting and ending with the dry ingredients. Mix only until just incorporated.
Pour the batter into the prepared pans, smooth the tops, and gently tap the pans on the counter to release air bubbles.
Bake on the middle rack for 25 minutes or until a toothpick comes out clean. Start checking at 18-20 minutes.
Cool the cake layers in the pans for about 10 minutes, then turn them out onto cooling racks and let them cool completely.