PREHEAT oven to 350° F. Grease and flour one 13 x 9-inch or two 9-inch round baking pans.
BEAT sugar and butter in large mixer bowl. Add flour, milk, water, eggs, lemon juice, vanilla extract, baking powder, baking soda and salt; beat on low speed until blended. Beat on high speed for 2 minutes. Beat in Choco Bake. Pour into prepared baking pan(s).
BAKE for 30 to 35 minutes or until wooden pick inserted in center comes out clean. Cool pan(s) for 20 minutes; invert onto wire rack(s) to cool completely. Frost with Chocolate Buttercream Frosting.
FOR CHOCOLATE BUTTERCREAM FROSTING:
MICROWAVE Choco Bake and butter in uncovered, microwave-safe bowl on HIGH (100%) power for 30 seconds; stir. If necessary, microwave at additional 5- to 10-second intervals, stirring just until butter is melted.
TRANSFER mixture to small mixer bowl; cool to room temperature.
BEAT sugar, 4 tablespoons milk, vanilla extract and salt into chocolate mixture just until spreading consistency. Up to 2 tablespoons milk can be added for a creamier frosting.