Preheat oven to 350° F. Grease and flour (or dust with extra cocoa) two 9-inch round baking pans.
In large mixer bowl beat butter, sugar and vanilla extract until creamy. Add eggs and food coloring; blend well.
Stir together flour, cocoa and salt; add alternately with buttermilk to batter mixture, beating until well blended.
In a small bowl, stir baking soda into vinegar; fold carefully into batter (do not beat). Pour batter into prepared pans. Bake 30-35 minutes or until wooden pick inserted in center comes out clean.
Cool 10 minutes; remove from pans to wire racks. Cool completely.
Thaw ice cream until soft, but not melted about 15 minutes at room temperature). Place in bowl and stir until smooth. Line a 9-inch cake pan with plastic wrap and fill with ice cream, packing down and smoothing top. Place in freezer until firm.
To make the frosting: Cream butter and shortening with electric mixer. Add vanilla extract. Gradually add sugar, 1 cup at a time, beating well on medium speed. Scrape sides and bottom of bowl often. When all sugar has been mixed in, icing will appear dry. Add milk and beat at medium speed until light and fluffy.
Use immediately, or keep icing covered with a damp cloth until ready to use.
To assemble cake: Place one cake layer on serving plate. Remove and unwrap ice cream layer; place on cake, place remaining cake layer on top. Frost top and sides with buttercream frosting.
Servings: 10-12