Preheat the oven to 350 degrees F. Spray 3 6-inch cake pans with non-stick cooking spray and line with circle cuts from parchment paper.
In a bowl, sift together the baking soda, salt, and flour. Set aside.
In another bowl, sift the cocoa powder. Add the red food coloring, apple cider vinegar, vegetable oil, and vanilla extract to the bowl. Mix well and set aside.
Using a handheld or stand mixer fitted with the paddle attachment, beat the butter and sugar together on a medium-high speed for 3 minutes. Add the eggs, one at a time. Scrape down the sides of the bowl with a rubber spatula, if needed.
Next add the cocoa powder mixture and mix until well combined. Reduce the speed to a medium-low and alternate between adding the dry ingredients and buttermilk until fully incorporated.
Divide the batter among the 3 prepared cake pans. Bake the cake for 25 to 35 minutes or until inserted toothpick comes out clean. Cool the cake completely before assembling and frosting the cake.