Start with ingrediencies: 4 cups of blackberries, 1 cup of white sugar, 2 tablespoons of cornstarch, 1/4 teaspoon of ground cinnamon, 1/4 teaspoon of ground allspice, 1/2 teaspoon of lemon juice. Steps 1 and 2: Step 1 Mash blackberries in a saucepan with a potato masher. Stir in sugar until juices form; place about 1..