Prepare the Ingredients: Wash the blackberries thoroughly if fresh, or thaw and drain if frozen. Zest the lemons and juice them.
Simmer the Berries: In a large saucepan, combine blackberries, lemon juice, lemon zest, and water. Cook over medium heat for about 10 minutes, stirring occasionally until the berries break down.
Add Sugar and Spices: Stir in the sugar, cinnamon, and ginger (if using). Continue simmering for about 20 minutes or until the mixture thickens, stirring occasionally.
Test for Doneness: To test, place a spoonful of jam on a cold plate. If it sets and doesn’t run when you run your finger through it, it’s done. If not, simmer for a few more minutes and test again.