Blueberry-Blackberry Jam 1 1/8 pounds blueberries 1 1/8 pounds blackberries the juice of a lemon 3 1/8 cups sugar Wash the fruit, drain it, and put it in a bowl. Sprinkle the lemon juice and the sugar over it, and let it rest for 24 hours. When it has rested, transfer it to a pot and simmer it over a gentle flame until a drop of jam on an inclined plate doesn’t run. Transfer the jam into sterile jars, seal them, sterilize them, and put them in your pantry when they have cooled. Yield: several jars of blueberry-blackberry jam.