Line 3 (8-inch) cake pans with parchment paper; coat with cooking spray. Set pans aside.
Sift together flour and next 3 ingredients.
Combine milk and butter in a 2-cup glass measure. Microwave at HIGH 1 to 1 1/2 minutes or until mixture is very hot.
Beat eggs and 1 1/2 cups sugar with a mixer at high speed 5 minutes or until egg mixture is pale yellow and thick. Add flour mixture, milk mixture, and vanilla. Beat 30 seconds or until well combined (batter will be thin). Quickly pour batter evenly into prepared cake pans.
Bake at 350° for 18 to 20 minutes or until cake starts to pull away from sides of pan and springs back when pressed in the center. Cool in pans on wire racks 10 minutes. Remove from pans, and cool completely.
Combine espresso granules, coffee liqueur, remaining 2 tablespoons sugar, and 3 tablespoons water in a 1-cup glass measure. Microwave at HIGH 1 minute or until sugar dissolves. Brush coffee mixture over cake layers,
Place 1 cake layer on a cake plate. Spread with about 1 cup whipped topping; sprinkle with 1/4 cup chopped toffee bars. Repeat procedure twice with remaining ingredients, ending with toffee bars.