Preheat the oven to 175°C / 350°F and line two 22 cm cake rings with parchment paper.

Whisk 3 eggs with 100 g all-purpose flour, 30 g cocoa powder, 100 g caster sugar, 4 g baking powder, and 80 g melted unsalted butter until smooth.

Divide the chocolate sponge batter between the prepared rings and bake for 18 min.

Cool the sponge layers completely, then level them if needed.

Brush both sponge layers with 100 ml orange juice mixed with 5 ml vanilla extract.

Cover 60 g orange peel with fresh water in a saucepan and bring it to a boil.

Drain the peel and repeat the fresh-water boiling process two more times to reduce bitterness.

Simmer the blanched peel with 135 g caster sugar, 135 ml water, and the split vanilla bean until translucent, about 35 min.

Pat the candied peel dry and coat it with 25 g caster sugar and 1 g citric acid.

Blend 200 g orange segments with 100 ml orange juice until smooth.

Heat the orange mixture with 60 g caster sugar, then dissolve 7 g bloomed gelatin powder into it.

Chill the orange gel until set, then reserve a portion for decoration.

Pour 200 ml hot heavy cream over 200 g dark chocolate and stir until a silky ganache forms.

Spread the ganache over one soaked sponge layer and chill it for 15 min.

Spread the set orange gel over the chilled ganache, keeping a narrow border around the edge.

Melt 200 g dark chocolate with 100 ml whole milk and cool the mixture until barely warm.

Whip 400 ml heavy cream to soft peaks and fold it into the cooled chocolate mixture.

Pipe or spread the dark chocolate mousse over the orange layer and place the second soaked sponge on top.

Freeze the assembled cake until firm, for at least 60 min.

Melt the remaining 100 g dark chocolate with 50 ml heavy cream to make a pourable glaze.

Unmold the frozen cake and pour the chocolate glaze over the top and sides.

Decorate with chocolate curls, candied orange peel, orange gel, edible yellow flowers, and edible chocolate balls.

Refrigerate the cake for 4 hours before slicing and serving.