Chocolate Cake

Praline paste
150g sugar
75ml water
150g hazelnuts
if it is difficult to process the caramelized hazelnuts into paste, add 1 - 2 tsp neutral flavour oil
Chocolate sponge cake (pan size: 36 x 22cm or 14 x 9 in)
30g dark chocolate
30g butter
40g (ml) milk
3 egg yolks
30g cake flour (or all purpose flour)
15g cocoa powder
3 egg whites (I'm sorry. There is a typo in a video, it's actually 3 egg whites instead of 4)
60g sugar
Chocolate mousse
55g - 65g dark chocolate
35g hot heavy cream