Preheat oven. Preheat the oven to 350 degrees F.
Make the Cake Batter. Cream the butter and sugar in a large mixing bowl. Add the eggs, one at a time beating well. Mix together the dry ingredients and set aside. In a separate bowl, combine the buttermilk, vanilla and food coloring. Alternate adding the dry and wet ingredients to the creamed butter until completely incorporated. Dissolve the soda in the vinegar and stir into the batter. Pour the batter into two 9-inch sprayed or buttered and floured cake pans. Bake in a preheated 350* oven for 30-35 minutes.
Prepare cake pans. Cut 2 rounds of parchment paper to fit inside 2 9-inch cake pans. Spray the pans with cooking oil and dust each with flour, shaking out any excess. Pour the cake batter evenly between the two pans.
Bake the red velvet cakes. Place each cake pan onto the center rack of your oven, close the door, and bake for 30-35 minutes, or until an internal thermometer reads 195-200 degrees F (this is the perfect baked temperature for moist cakes). Remove from the oven and cool completely before carefully turning the pans over and removing the cakes.
Make the Ermine Frosting. In a medium sized saucepan, heat the milk, flour, salt and sugar, over medium high heat. Bring to a boil while whisking consistently until the paste reaches the consistency of pudding. Set aside and let cool completely. In a mixing bowl, whip the butter until smooth and slightly lightened in color. Beat in the cooled milk mixture along with the vanilla. The frosting should puff up and become silky smooth.
Frost the cake. Place one cooled cake round down on your serving platter. Top with half of the frosting and smooth with a spatula. Place the second cake round centeres on top of the first. Top with the remaining frosting and decorate as desired.