Whisk the eggs and sugar in a bowl until the mixture triples in volume and turns a pale yellow color.
Gently fold the sifted flour into the egg mixture using a spatula, being careful not to deflate the batter.
Grease a cake tin and bake the sponge base at 170 degrees Celsius for 20 minutes.
Prepare the mousse by melting the chocolate over a bain-marie, then allow it to cool to lukewarm.
Whip the heavy cream until it reaches soft peaks.
Fold the melted chocolate into the whipped cream using a gentle motion to maintain volume.
Dissolve the gelatin in a small amount of warm water and temper it into the mousse mixture.
Place the sponge base at the bottom of a springform pan.
Pour the mousse over the sponge and smooth the surface evenly.
Chill in the refrigerator for at least 4 hours until the cake is fully set.