Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.

In a mixing bowl, combine the eggs and granulated sugar. Beat with an electric mixer for about 5 minutes until the mixture is pale and fluffy. Add vanilla extract.

Gently sift the flour and cocoa powder over the egg mixture. Fold them in carefully with a rubber spatula until just combined.

Pour batter into the prepared cake pan and smooth the top. Bake for 15 minutes or until a toothpick comes out clean. Allow the cake to cool completely in the pan.

Once cooled, carefully remove the cake from the pan and cut it into two equal layers horizontally.

In a shallow dish, combine the brewed espresso and coffee liqueur. Dip each layer of the cake into the mixture briefly to soak.

In another mixing bowl, combine mascarpone cheese and powdered sugar, and mix until smooth. In a separate bowl, whip the heavy cream until soft peaks form. Gently fold the whipped cream into the mascarpone mixture.

Place one layer of the soaked cake onto a serving plate. Spread half of the mascarpone mixture on top. Add the second layer of the soaked cake and spread the remaining mascarpone mixture on top.

Sift cocoa powder over the top for dusting. Garnish with dark chocolate shavings if desired.

Refrigerate for at least 4 hours before serving to allow the flavors to meld. Slice and enjoy!