Preheat oven to 350 degrees F (175 degrees C). Butter and flour three 6-inch cake pans.
In a medium bowl, whisk together the flour, salt, and baking soda.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla.
In a small bowl, whisk together the cocoa powder, buttermilk, vinegar, and red food coloring.
Add the flour mixture and buttermilk mixture to the butter mixture alternately, beginning and ending with the flour mixture. Beat until just combined.
Pour the batter into the prepared cake pans and bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.