Put the raspberries in a bowl and sprinkle with the sugar and one tablespoon of water. Leave at room temperature for an hour. The sugar should have dissolved, and some liquid should have come out of the raspberries. Add the mixture to a fry pan and bring the mixture to the boil and simmer for about five minutes so that the raspberries are breaking down and most of the liquid has evaporated. Leave to cool then serve with any dessert of your choice or transfer to the fridge in a tightly covered container until needed.