Prepare the Espresso Soak: Brew 1½ cups of strong espresso and let it cool slightly. Add 2 to 4 tablespoons of coffee liqueur (optional, or use 1 teaspoon pure vanilla extract or coffee-flavored syrup for an alcohol-free version). Pour the espresso mixture into a wide, shallow dish.

Make the Mascarpone Cream: Combine 4 large egg yolks and ½ cup (100 grams) granulated sugar in a double boiler. Whisk constantly over simmering water until the mixture becomes pale, thick, and reaches about 160°F (71°C) to create a sabayon. Remove from heat and let the sabayon cool for a few minutes. Gently fold in 1 pound (450g) of room temperature mascarpone cheese until smooth and lump-free. In a separate bowl, whip 1 cup (240ml) heavy cream until stiff peaks form. Fold the whipped cream into the mascarpone mixture in batches to maintain volume and creaminess.

Assemble the Layers: Choose an 8 or 9-inch round baking dish or cake ring. Spread a thin layer of the mascarpone cream on the bottom to anchor the base. Dip each ladyfinger or sponge slice briefly (1 to 2 seconds per side) in the espresso mixture, avoiding oversoaking. Layer the soaked ladyfingers or sponge tightly across the bottom of the dish. Spoon a generous layer of mascarpone cream over the soaked base and spread evenly. Repeat the layering process (soaked cake/ladyfingers followed by cream) until you reach the top, finishing with a thick final layer of mascarpone. Smooth the surface using an offset spatula.

Chill and Set: Cover the cake with plastic wrap and refrigerate for at least 6 hours, though overnight is best, to allow the flavors to meld and the texture to firm up. Before serving, dust the top liberally with unsweetened cocoa powder using a fine-mesh sieve. Optionally, garnish with chocolate curls, grated dark chocolate, or coffee beans.