Below is a recipe you can use, but I think you can safely play with the ingredients and ratios. The gist is that you are combining the berries, liquid and sugar, bringing them to a boil, reducing to a simmer, cooking down a bit, and finally straining. Good luck.

4 1/2 cups blackberries (1 1/2 pounds)
1 cup sugar
1/2 cup water
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preparation

Bring berries, sugar, and water to a boil over moderately high heat, stirring until sugar is dissolved. Reduce heat and simmer, uncovered, stirring occasionally, until fruit is soft, about 30 minutes. Pour mixture through sieve into a bowl