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 tablespoon blackberry juice in a small bowl and stir in cornstarch. Pour cornstarch mixture into saucepan.
  • Step 2 Bring berries to a boil, stirring often, until jam is thickened, about 15 minutes. Stir in cinnamon and allspice. Remove from heat and allow to cool. Transfer jam to a bowl, cover, and refrigerate until chilled. Stir in lemon juice.