Stir together the ingredients in a medium pot. Start out using 1/4 cup of maple syrup.
Simmer the ingredients, covered, over medium-low heat. The mixture will become quite watery as the berries break down. Remove the cover at this point and continue simmering until you have the consistency you want.
Taste the mixture. Unless you’re using very sweet berries, it will probably be tart. Add up to another 1/4 cup of maple syrup. Continue simmering until you have a slightly thickened sauce with a flavor you like.
Optional: If you want a thicker berry sauce, add a teaspoon or two of arrowroot (or other) starch. Mix in the starch with a whisk, and continue to whisk over medium-low heat until thickened to your liking.