Knead the flour, sugar, salt, egg yolk, cocoa and butter in pieces, first with the dough hooks of the hand mixer, then with your hands to a smooth dough. Wrap dough in cling film and chill for approx. 30 minutes.
Grease the tart mould (24 cm Ø at the top edge, 20 cm Ø at the bottom). Roll out the dough on a floured work surface (approx. 28 cm Ø). Line the mould with the dough. Press down the rim and cut off any excess dough. Prick the dough several times with a fork. Put baking paper on the dough, fill in dry peas. Bake in the preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for about 15 minutes.
Remove dry peas with the baking paper. Bake for another 10-15 minutes, let cool down. In the meantime, roughly chop the chocolate and chocolate coating. Heat the cream and liqueur. Add chocolate and couverture and melt in it. Let the chocolate cream cool down a little, then fill into the mould. Chill the Chocolate Tart for at least 4 hours.
Peel approx. 50 g of the room-warm white chocolate with a peeler and put it in a cool place. Before serving, decorate the chocolate tart with chocolate rolls and dust with cocoa.