Here's a recipe I ran across that may help

Chocolate Dome
FOR THE MOUSSE
62 gm Bitter chocolate
62 gm Butter
10 gm Gelatine
4 x Eggs
7 gm Sugar substitute powder
75 ml Cold water
25 gm Cocoa powder
265 ml Cream, lightly whipped
Chocolate sponge to line the moulds
FOR THE GLAZE
20 gm Gelatine
40 ml Water
100 gm Cocoa powder
45 gm Sugar substitute powder
300 ml Water
300 ml Single cream

CHOP the bitter chocolate and melt both chocolate and the butter together in a heavy bottomed pan. Mix well and keep aside to cool.

Soak the gelatine in 60 ml water. Whip the eggs till they are light and stiff. Meanwhile put the sugar substitute powder and 15 ml water in a pan and keep stirring over low heat till the sugar dissolves and you obtain a thick syrup. Slowly pour this syrup in a string over the eggs and continue to whip. Melt the gelatine and gradually pour over the eggs. Keep whipping Then lightly fold in cocoa powder, followed by melted chocolate and butter mixture. Finally fold in the whipped cream.

Fill the mousse in dome shaped chilled moulds, leaving half cm on top. Cut the chocolate sponge into rounds with a spare mould and place on top of the mousse. Chill in the deep freezer. Glaze and serve chilled.

To finish: Demould the mousse onto a wire rack. Pour the warm glaze on top to coat it evenly. Remove onto a cold plate and decorate as required. You can use tempered chocolate and make it into a thin sheet, break into pieces and put on all sides of the mousse.

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and a few more pics: