Sit a large sieve over a bowl and tip in the cherry compote. Leave to drain for 2 hours.
Preheat the oven to 400°F. Line a deep, 7–8 inch cake tin with non-stick baking parchment. Put 7 oz of the chocolate into a saucepan and add the butter with 4 fl oz cold water. Place over a low heat until melted.
Mix the dry ingredients in a large bowl and stir in the orange zest, melted chocolate, eggs and yogurt. Pour this into the lined cake tin and bake in the preheated oven for 1½ hours or until a skewer pushed into the centre comes out clean. Leave to cool in the tin.
Pour the drained compote liquid into a small saucepan with the orange juice and Grand Marnier. Bring to the boil and bubble until reduced to about 6 tablespoons. Leave to cool.
Put the remaining chocolate into a saucepan, add 2 tablespoons of the reduced cherry liquid and the double cream. Leave over a low heat until the chocolate has melted. Stir until smooth, then cover and chill the cherry ganache for 30 minutes.
Cut the cake into 3 layers. Drizzle the bottom layer with some of the remaining cherry liquid, spread with a quarter of the ganache and scatter over half of the drained cherries. Sandwich the second layer on top and repeat with the remaining cherry liquid, another quarter of the ganache and the rest of the cherries. Top with the final layer, spread the remaining ganache over the top of the cake and decorate with grated chocolate or chocolate curls.
Makes 12–14 slices