Heat berries and sugar over low heat, stirring occasionally. Simmer 10 minutes.
Add lemon juice and let cool.
Put strainer over a bowl and pour mixture into strainer. Using the back of a wooden spoon press on the berries to extract as much juice as possible. Discard seeds and pulp.
Store in a glass jar. Will keep in the fridge for months (possibly forever).
Serve on pancakes, ice cream, brownies, custard or any dessert.