Melt the butter and mix with the crumbled shortbread biscuits. Pour the first layer into the glass and flatten with a spoon. Then, halve the yoghurt in two bowls (250 g (8.9 oz) each) and mix each with bilberries or raspberries so that the yoghurt colours. Then layer in the glass one after the other and add berries if wanted. Then decorate the top with crumbles.