Preheat oven to 350 degrees F.
Grease 3, 8-inch cake pans and line the bottom with parchment paper. This helps the cake to not stick and is worth the extra effort.
In a medium bowl cream the butter and sugar until fluffy, about 3 minutes, scraping the sides as needed.
Add eggs and mix until well combined.
In a small bowl mix the red food coloring with cocoa to make a paste, you can use a fork to combine it well.
Add the food coloring mixture to the bowl with the whipped butter and beat to combine.
Add the salt and 1 cup of flour and mix just until combined.
Add ½ cup buttermilk and vanilla and mix until the mixture just comes together.
Add 1 cup flour and mix just until combined.
Add remaining buttermilk and mix until a smooth batter forms.
Add remaining flour and mix to combine.
Add vinegar to the baking soda and immediately add to mixture. Mix thoroughly.
Divide between the cake pans, smooth out the tops with a spatula, and bake for 25-30 minutes or until the cakes spring back lightly when touched.
Let the cakes cool in the pans for 5 minutes and then run a knife around the ends of the pan and flip the cakes out onto cooling racks. Let the cakes cool before frosting.