Prepare the Egg Mixture: Set up a double boiler over medium heat and whisk together the egg yolks and granulated sugar for about 5 minutes until pale and thickened.

Whip the Egg Mixture: Transfer the cooled egg mixture to a stand mixer and beat on medium-high speed for 5 to 7 minutes until light and airy.

Melt the Chocolate: Gently melt the semi-sweet chocolate until smooth and stir it into the whipped egg mixture gradually.

Prepare the Cream Mixture: In a separate bowl, whip heavy cream and mascarpone until soft peaks form, then sift in cocoa powder and fold.

Combine Cream and Chocolate Mixtures: Gently fold the whipped cream into the chocolate-egg mixture until just combined.

Assemble the Layers: Dip ladyfinger cookies in coffee and arrange in a dish, spreading half of the chocolate cream over them.

Add the Second Layer: Repeat dipping and layering, then top with remaining chocolate mascarpone cream.

Chill and Set: Cover with plastic wrap and refrigerate for at least 4 hours or overnight.

Decorate Before Serving: Whip additional mascarpone, heavy cream, and powdered sugar, then dust with cocoa powder before serving.