Preheat oven to 350 degrees.
Grease and flour two 8-inch cake pans, set aside.
In a medium bowl combine flour, cocoa powder, salt and baking soda, set aside.
In another bowl combine buttermilk, vinegar, and vanilla extract, set aside.
Beat butter and sugar until light and fluffy.
Add eggs, one at a time, beating well after each addition.
Adjust mixer speed to low and carefully add the red food coloring.
Add dry and wet ingredients alternately, beginning and ending with dry ingredients, stopping to scrape the bottom and sides of the bowl a time of two. Mix until combined, but do not overmix.
Pour the batter into the prepared cake pans.
Bake at 350℉ for 35 to 40 minutes or until a toothpick inserted in the center comes out clean.
Cool in pan, on a cooling rack for 10 - 15 minutes. Turn out on cooling rack and allow to cool completely.
While the cake is cooling prepare the frosting. Combine butter and cream cheese in a mixing bowl. Add vanilla and powdered sugar, beating until combined. Add enough milk to reach spreading consistency. Stir in pecans.
Place one cake layer on serving plate. Spread frosting over the top of cake.
Place second layer on top of first. Frost top and sides of cake.
Store in refrigerator.