Rhubarb and raspberry trifle

Toss raspberries and rhubarb in sugar and leave to soak for about 2 hours.
Place in a saucepan and simmer over low heat until fruit is tender.
Strain off fruit juices into a small saucepan (there will be 250-400 ml). Stir in gelatine (7 ml (1 1/2 tsp)) for 250 ml or 15 ml (3 tsp) for 400 ml) until dissolved.
Refrigerate until set. Cut into cubes or break up with a fork.
Mix yoghurt and mascarpone cheese. Toss cake cubes in liqueur.
Layer ingredients in 6 glasses in this order: jelly, cake, yoghurt mixture. fruit, yoghurt mixture. Sprinkle each dessert thickly with sugar (about 30 ml (2 tbsp) per dessert) and caramelise under a heated grill.