Method
1. Add granulated sugar and egg yolk to a clean stand mixer bowl
2. Beat until triples in volume
3. Transfer content of stand mixer bowl to large mixing bowl
4. Clean stand mixer bowl then set aside
5. Add granulated sugar and heavy cream to a clean medium bowl
6. Beat until soft peaks form
7. Add mascarpone cheese to the medium bowl
8. Beat until peaks form
9. Fold mixture into egg mixture gently
10. Add espresso and Cognac to a clean small bowl and mix
11. Dip sponge fingers into the mixture one by one
12. Dust a clean 2-quart baking dish (an 8x8-inch dish, or a 9-inch round cake pan would also work here) with 1 tablespoon cocoa powder
13. Transfer ladyfingers into baking dish
14. Repeat, using half the ladyfingers, until you’ve got an even layer, breaking the ladyfingers in half as needed to fill in any obvious gaps
15. Add half of mascarpone mixture to ladyfingers
16. Repeat with remaining espresso-dipped ladyfingers and mascarpone mixture
17. Dust with unsweetened cocoa powder
18. Garnish with bittersweet chocolate
19. Cover with plastic wrap
20. Let rest in fridge - approx 4 hr
21. Serve