Preheat the oven to 180 °C (350 °F). Beat the eggs and sugar at maximum speed for 10 minutes. Sift the cacao and flour on top of the egg mixture and fold in gently with a spatula. Spread the batter evenly in an 18 cm cake pan lined with parchment paper (the bottom), and bake for 15 minutes. After a few minutes, take the baked sponge out of the cake pan and place it on a cooling rack to cool.
While baking the sponge, prepare the sugar solution and the strawberry purée: bring the strawberries with sugar to a boil, blend with an immersion blender and cool until lukewarm.
While the sponge is cooling, prepare the chocolate filling. Melt the cho- colate and 100 g whipping cream in a double boiler, whip the rest of the cream (250 g) and refrigerate. Soak gelatin sheets in cold water for at least 5 minutes. Dissolve the wrung-out gelatin in the melted chocolate and add the strawberry purée and strawberry extract. Stir with a spatula to combine the ingredients, remove from steam and cool until lukewarm. Fold the whipped cream into the lukewarm chocolate with a spatula.
Cut the sponge into two equal layers; cut the top layer to a 14 cm circle (4 cm less than the diameter of the cake). Place the bottom, bigger part of the sponge cake on a stand, moisten it and fit the ring. Coat with slightly less than half of the filling and level out the surface. Place the smaller sponge in the middle and moisten. Spread on the rest of the filling – fill the space around the sponge first, level out the surface and refrigerate to set.
Once the filling has chilled, glaze with the chocolate glaze: bring the cream to a boil and pour it over the chocolate. Wait one minute, then mix with a spatula until smooth. Cool slightly and pour over the filling.
Chill the cake for at least 5 hours before serving. Once chilled, remove the ring and decorate as desired.