1. Brew the espresso coffee and let it cool down.
2. When it is at room temperature, mix it with the liquor and vanilla, and pout it in a shallow container.
3. In a mixing bowl, combine the mascarpone cheese, 1/2 cup of sugar and the whipping cream, and mix it with a hand mixer into a smooth cream, about 2 minutes.
4. Place the egg whites in a separate bowl and start beating, while adding the rest of the sugar and the lemon juice.
5. Beat the egg whites to stiff peaks. Before you start beating, make sure that the mixer and the bowl are completely clean, otherwise you may not be able to beat the whites to stiff peaks.
6. Fold the egg whites slowly into the mascarpone mixture.
7. Spread some of the mixture on the bottom and the sides of a 12-inch cake form with a removable ring.
8. Cut 10 savoiardi biscotti to half, dip them briefly (for 2 seconds) in the coffee, and arrange them standing on the inside of the cake ring.
9. For the bottom use whole biscotti, dip them in the coffee mixture and arrange them horizontally.
10. Cut some of the biscotti to size, if necessary.
11. Cover with 1/3 of the mascarpone mix.
12. Repeat 2 more times. The inside of the tiramisu should have 3 layers of biscotti.
13. Top the tiramisu with the remaining mascarpone cream.
14. Grate the chocolate over the tiramisu.
15. Cover the cake and refrigerate for at least 5 hours before serving.