Put all the ingredients into a medium size pan and mix gently with a wooden spoon so the berries become thoroughly coated with sugar and cornflour.
Set the pan on low and stir frequently until the juices start to run, then increase the heat slightly and simmer gently until the fruit has softened and the juices have thickened to make a sauce. Keep stirring often as the fruit cooks.
Taste the sauce and add more sugar if you want it a bit sweeter. Serve hot, warm or cold.