1. For the Cake:
2. Preheat oven to 350F. Lightly grease 2 (8 ) round cake pans; line with wax paper. Lightly grease wax paper. Dust pans with flour; shake out excess, and set aside.
3. Beat cake mix, next 3 ingredients, and 1 cup water in a large bowl at low speed with an electric mixer about 30 seconds; then beat at medium speed 2 minutes. Pour batter into prepared pans.
4. Bake at 350F for 28 to 30 minutes or until a wooden pick inserted in center comes out clean. Let cool in pans on wire racks 10 minutes; remove from pans. Discard wax paper, and cool layers completely on wire racks (1 hour). Wrap and chill cake layers 1 to 24 hours. (This step enables you split layers with ease.)
5. Using a serrated knife (or a wire cutter made specifically for this job), slice layers in half horizontally to make 4 layers. Place 1 layer, cut side up on a cake plate. Brush with one-fourth of Cinnamon-Espresso Syrup (see below). Spread with 1-1/2 cups Mascarpone Frosting (see below); sprinkle with one-fourth chopped chocolate-covered toffee pieces. Repeat process with remaining 3 layers, syrup, frosting, and chopped candy bar. Frost sides of cake with remaining 1-1/2 cups frosting. Garnish, if desired. Cover and refrigerate overnight. Store in refrigerator.
6. For the Cinnamon-Espresso Syrup:
7. Bring 1 cup water, sugar, and cinnamon stick to a boil in a small saucepan; boil 1 minute. Remove from heat; let stand 15 minutes. Remove and discard cinnamon stick. Stir in espresso powder and liqueur.
8. For the Mascarpone Frosting:
9. Beat first 3 ingredients at low speed with an electric mixer until creamy. Gradually add Cinnamon-Espresso Syrup, beating until smooth. Fold in whipped cream. Cover and chill until ready to use.
10. This towering cake is best when made ahead so the flavors can meld.