For the filling, chop 300 g caramel sweets. Boil up with the cream while stirring. Simmer for about 10 minutes until the candies are dissolved. Let the toffee cream cool down in a mixing bowl. Chill for about 2 hours.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). For the dough melt butter and let it cool down a little. Mix flour, sugar, cocoa, vanilla sugar, 1 pinch of salt and baking powder.
Finely chop the chocolate. Beat the eggs with the whisk of the mixer until creamy. Add liquid butter while stirring. First stir in flour mixture, then chocolate.
Line a baking tray with baking paper. 13-14 Place heaps of dough on the baking tray with a little space between them (they run apart during baking). Bake in a hot oven for about 10 minutes until the edges form a light crust.
Take it out. First cool down on the tray for about 5 minutes, then remove from the tray together with the paper, let it cool down. Bake a total of about 40 whoopie halves from the dough.
Halve the toffee cream, whip until creamy and allow 1 packet of cream stiffener to trickle in. Finely chop 50 g caramel sweets and fold into both toffee creams. Pour into a piping bag with a large perforated spout.
Spray onto the smooth underside of about 20 whoopie halves. Place the remaining halves on top with the flat side as a lid. Chill for at least 30 minutes.
Coarsely chop the chocolate coating, melt in a hot water bath and let it cool down a little. Coarsely chop the hazelnuts. Put a small spot of chocolate coating on each Whoopie Pie and sprinkle with nuts. Keep cool until serving.