You can buy individual heart-shaped pierced moulds imported from France in good kitchenware shops. Like much kitchenware, they are worth looking out for when you are in France, as they tend to be cheaper. Line the moulds with damp muslin or cheesecloth to stop the mixture drying out too much. If you cannot obtain moulds, pierced yoghurt or cottage cheese cartons are a good substitute, but you will, of course, lose the heart shape. I use the pink, tender, forced rhubarb in this recipe.