Preheat the oven to 350°F (175°C). Line two 9-inch round cake pans* with parchment paper and spray with a cooking spray.
In a medium bowl, whisk together flour, sugar, cocoa and salt. Set aside.
In a large mixing bowl, beat the eggs, vegetable oil, buttermilk, red food coloring, and vanilla extract until well combined.
Add the flour mixture and mix the batter until smooth, about a minute.
In a small dish, mix together baking soda and vinegar. While the soda/vinegar mixture is bubbling, add it to the batter and mix well.
Evenly divide the batter between the two cake pans. Bake the cakes for about 30 minutes, or until the inserted toothpick comes out clean. If the toothpick comes out with moist crumb, bake for a minute longer and test again. Be careful not to overbake the cakes, or they'll dry out.
Cool the cakes in the pan for 5 minutes, then invert them onto a wire rack to cool completely, for couple of hours or overnight. (Wrap the cakes in a plastic wrap, if you're resting overnight.)