For the chocolate cream, chop the couverture. Boil up the cream. Remove from heat, melt the chocolate coating in the cream. Stir in 50 g butter, mix with a whisk to a smooth mixture. Pour the chocolate cream into a bowl, cover and leave to cool for about 2 hours.
Fill the sponge fingers into the freezer bag, close the bag tightly and crumble the sponge fingers with a rolling pin. Mix with hazelnuts and baking powder. Melt 150 g butter and let it cool down a bit.
Grease a fat pan (deep baking tray; 32 x 39 cm) and dust with flour. Preheat the oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer).
Beat the eggs, 175 g sugar, vanilla sugar and 1 pinch of salt with the whisk of the mixer for 8-10 minutes until thick and creamy. Carefully fold in the crumb-nut mixture and the liquid butter. Fill the dough into the fat pan and smooth it down.
Bake in a hot oven for 25-30 minutes. Remove and let cool.
For the spiders, carefully unroll liquorice snails and cut each into 6 equally sized pieces. Place 3 liquorice sections on top of each other, slightly offset in the middle, with a little chocolate cream on top of each other, press them down a little.
Stick 1 praline on each with a little chocolate cream. Halve the liquorice confectionery rolls and attach them to the praline with some chocolate cream as eyes. Let the spiders dry.
Spread the rest of the chocolate cream on the cake. Chill for about 30 minutes. Cut the cake into pieces and decorate with the spiders.