Combine a half-pint of raspberries, all the blueberries, sugar, zest and 1/3 cup water in a saucepan and bring to a boil. Lower the heat and cook uncovered over medium-low heat, stirring occasionally, for 8 to 10 minutes. The juice will become a syrup and the berries will be slightly cooked. Off the heat, stir in the remaining raspberries and the framboise, if desired.
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