Grease a 15x10x1-inch baking pan; set pan aside. In a medium saucepan combine butter, water, and cocoa powder. Bring to boiling, stirring constantly. Remove from heat.

In a large mixing bowl combine flour, sugar, soda, salt, and cinnamon (if desired). Add eggs, buttermilk, and vanilla. Beat with an electric mixer on low to medium speed to combine. Add cocoa mixture and beat until blended. Pour batter into prepared pan.

Bake in a 375 degree F oven 20 minutes or until cake springs back when lightly touched.

Immediately pour hot Chocolate Frosting over warm cake; spread evenly. Completely cool cake in pan on a wire rack. Cut into squares. Makes 60.

In a medium saucepan stir together 1/4 cup butter or margarine, 3 tablespoons unsweetened cocoa powder, and 3 tablespoons buttermilk. Cook and stir until boiling; remove from heat. Beat in 2-1/4 cups sifted powdered sugar and 1/2 teaspoon vanilla with an electric mixer on low speed until blended. Stir in 1/2 cup chopped walnuts.

Prepare and bake cake as directed; cool completely. Do not frost. Place in a freezer container or bag. Freeze up to 1 month. Before serving, thaw several hours at room temperature. Frost as directed.