Put berries and 2 tablespoons of water in a sauce pot. Cook for about 15-20 minutes, stirring often over medium heat. The berries will burst, releasing their juices. To help with this process, as you stir, mash the berries against the sides of the pot.

Place a fine mesh strainer over a bowl. Pour the berries and juice through the strainer. Working with a mixing spoon or a rubber spatula, stir and press the berries against the strainer to express the juices through the strainer and into the bowl. There should be about 1 cup of juice from the berries. Discard the berry pulp and seeds.

Pour the 1 cup of berry juice back into the sauce pot.

Stir the cornstarch and the sugar together. Whisk them into the berry juice.

Over medium heat bring to a simmer, stirring constantly until berry juice mixture is somewhat thickened.

Stir in the cream. Continue to cook and stir until sauce is warm.

This sauce thickens as it cools, thin with additional cream, if desired. Serve slightly warm or at room temperature. Cover and refrigerate any left-over sauce. Warm before serving.