Add the raspberries to a saucepan over medium heat. If using frozen raspberries, stir occasionally until they’re thawed. Mash down the raspberries with a fork.

Meanwhile, dissolve the cornstarch or arrowroot powder with the cold water to create a slurry.

Add the slurry, maple syrup, and lemon juice to the pan. Bring to a simmer, stirring constantly, until the jam has thickened. Take off the heat, and once cool, refrigerate. It will thicken even more as it rests in the fridge.