In a saucepan over medium heat, stir together the berries and sugar. Cook over medium-low heat until the berries have mostly broken down, stirring occasionally to prevent the sugar from scorching. Don't over-reduce, or it will not remain spreadable. After about 20 minutes of simmering, place a small amount of the mixture on the plate from the freezer. Run your finger through it after a minute or so. If the mixture has gelled and does not run back together, the jam is done. If it is still runny, continue to cook.
