Line the base of a springform pan (26 cm in diameter) with baking paper, grease the sides and line with cling film.
Melt the chocolate and butter in a wide pan over a low heat, add the sugar, stir in the Cornflakes and hazelnuts. Transfer the mixture to the tin and press down gently. Cover and refrigerate for approx. 1 hr.
Combine the yoghurt, sugar and vanilla sugar. Dissolve the gelatine in the boiling water, mix together with 2 tbsp of the yoghurt mixture and immediately stir into the remaining mixture. Refrigerate the mixture until it is just set at the edges, then stir until smooth. Carefully fold in the whipped cream. Pour the mixture onto the cake base. Cover the cake and refrigerate for approx. 3 hrs. until set.
Remove the tin frame, slide the cake onto a platter. Mix the cherries with the honey, arrange on top of the cake, sprinkle with the pistachios, serve immediately.