Place the blueberries in a bowl and allow to thaw. Rinse a box mould (11 x 25 cm; 1.25 litre capacity) with water and cover with foil. Cut 8 butter wafers to size and line the bottom of the mould with them.
Coarsely crumble remaining wafers and sections.
Soak gelatine in cold water. Mix ricotta, yoghurt and sugar. Whip 250 g cream until stiff. Dissolve the gelatine, stir in 5 tbsp. ricotta yoghurt, stir into the remaining ricotta yoghurt. Carefully fold in the cream.
Drain blueberries well and stir into the cream with cookie crumbs, except for something to decorate. Pour into the mould and chill for at least 1 hour.
Chop the chocolate and coconut fat. Heat 150 g cream in a small pot. Melt chocolate and coconut oil in it. Let cool down for about 15 minutes. Pour on the cream and smooth it down. Put the cake in a cool place for another 1-2 hours.
Carefully lift the cake out of the mould, remove the foil and decorate with the remaining cookie crumbs.