Cake:
1 ½ cups white sugar
½ cup shortening
2 eggs
4 tablespoons red food coloring
2 tablespoons cocoa
1 cup buttermilk
1 teaspoon salt
1 teaspoon vanilla extract
2 ½ cups sifted all-purpose flour
1 tablespoon distilled white vinegar
1 ½ teaspoons baking soda
Icing:
1 cup milk
5 tablespoons all-purpose flour
1 cup white sugar
1 cup butter, room temperature
1 teaspoon vanilla extract
Preheat the oven to 350 degrees F (175 degrees C). Grease two 9-inch round pans.
Make the cake: Beat 1 1/2 cups sugar and shortening together in a large bowl with an electric mixer until light and fluffy. Add eggs one at a time, beating well after each addition. Combine red food coloring and cocoa to make a paste; add to creamed mixture.
Mix buttermilk, salt, and 1 teaspoon vanilla together in a small bowl. Add flour, alternating with buttermilk mixture, mixing just until incorporated. Mix vinegar and baking soda together; gently fold into cake batter and pour into prepared pans.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 30 minutes. Cool on a wire rack for 5 minutes. Run a table knife around the edges to loosen. Invert carefully onto a serving plate or cooling rack. Let cool, about 30 minutes.
Make the icing: Heat milk and flour in a saucepan over low heat, stirring constantly, until thick. Set aside to cool completely.
Meanwhile, beat sugar, butter, and vanilla together in a large bowl with an electric mixer until light and fluffy. Add cooled flour mixture and beat until frosting is a good spreading consistency. Frost cake layers when completely cool.