Let eggs and butter stand 30 minutes. Preheat oven to 350 degrees F. Grease and flour three 8 x 1 1/2-inch round baking pans; set aside.

In medium bowl combine flour, cocoa powder, and 3/4 tsp. salt; set aside. In large mixing bowl beat butter on medium-high 30 seconds. Add sugar and vanilla; beat until combined. One at a time, add eggs; beat on medium after each. Beat in food coloring on low.

Alternately add flour mixture and buttermilk to egg mixture; beat on low-medium after each just until combined. Stir together baking soda and vinegar. Add to batter; beat just until combined.

Spread in prepared pans. Bake 25-30 minutes or until pick inserted near centers comes out clean (cakes may appear marbled). Cool in pans on wire racks 10 minutes. Remove from pans; cool.

Prepare Buttercream Frosting. Place layer flat side up on plate. Spread top with 3/4 cup frosting. Stack layer, flat side up; spread top with 3/4 cup frosting. Stack final layer, flat side down; spread remaining frosting on top and sides. Makes 16 servings.

Buttercream Frosting: In medium saucepan whisk together 1-1/2 cups whole milk, 1/3 cup flour, and dash salt. Cook and stir over medium heat until thickened and bubbly. Reduce heat; cook and stir 2 minutes more. Transfer to small bowl; cover surface with plastic wrap. Refrigerate until cooled (do not stir). In large bowl beat 1-1/2 cups softened butter, 1-1/2 cups sugar, and 2 tsp. vanilla on medium 5 minutes until light and fluffy and sugar is almost dissolved. Add cooled milk mixture, 1/4 cup at a time; beat on low after each until smooth.