Beat shortening at medium speed with an electric mixer until fluffy; gradually add sugar, beating well. Add eggs, 1 at a time, beating until blended after each addition.
Stir in food coloring and vanilla, blending well.
Combine flour, salt, and cocoa; set aside.
Combine buttermilk, vinegar, and soda in a 4-cup liquid measuring cup. (Mixture will bubble.)
Add flour mixture to shortening mixture, alternately with buttermilk mixture, beginning and ending with flour mixture. Beat at low speed until blended after each addition. Beat at medium speed 2 minutes; pour batter into 3 greased and floured 8-inch round cakepans.
Bake at 350° for 25 minutes. Cool in pans on wire racks 10 minutes; remove from pans, and cool completely on wire racks.
Spread Cream Cheese Frosting between layers and on top of cake. Garnish with chopped pecans, if desired.
Sheet Cake: Pour batter into a greased and floured 13- x 9-inch pan. Bake at 350° for 30 minutes. Cool completely in pan on a wire rack. Spread cream cheese frosting on top of cake. Garnish, if desired. Yield: 1 (13- x 9-inch) cake.
Petit Fours: Pour half of batter into a greased and floured 15- x 10-inch jellyroll pan; chill remaining batter. Bake at 350° for 10 minutes or until center of cake springs back when lightly touched (do not overbake). Cool in pan on a wire rack 10 minutes; remove from pan, and cool completely on a wire rack. Repeat procedure with remaining batter. Reserve 1/2 cup Cream Cheese Frosting. Place 1 cake layer on a large cutting board or baking sheet; spread with remaining 3 cups frosting. Top with remaining cake layer; cover and chill. Using round cutter or knife, cut into 1 1/2 inch circles or squares. Pipe or dollop reserved 1/2 cup frosting on tops of cakes. Garnish with pecan halves, if desired. Yield: about 3 dozen.