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 if you have strict rules to prevent cross contamination).
Serve on pancakes, ice cream, brownies, custard or any dessert.
Notes
Here are some ways to enjoy this homemade sauce with links to the recipes.