1 pound rhubarb, trimmed and cut roughly 3/4-inch chunks OR 3 Cups frozen berries
3⁄4 cups sugar
2 tablespoons salted butter - optional
2 tablespoons orange juice - optional
1 tablespoon orange or lemon zest - optional
1. In a medium bowl, mix the rhubarb with the sugar.
2. In a heavy medium saucepan over medium heat, melt the butter. When the butter has melted, add the rhubarb and sugar mixture and the orange juice. Allow to cook, undisturbed, for 2 minutes. Then gently stir and continue to cook, stirring occasionally, until the rhubarb is tender and beginning to fall apart and its juices are thick, 10 to 15 minutes. For a thicker jam, keep cooking for up to an additional 40 minutes on low heat, stirring occasionally.
3. Remove from heat and let cool.
4. Store in an airtight container in the refrigerator for up to 1 week.