1. Defrost the berries.
2. Put them in a deep pan and add the lemon juice.
3. Cook over medium heat until the berries are really juicy, about 5 minutes.
4. Add the lemon zest.
5. Turn up the heat to medium-high and boil until the berries are soft, about 5 minutes.
6. Add the sugar and bring to a boul over medium-high heat.
7. Pout it into a heat-proof container and cool it to room temp.
8. It should thicken as it cools.
9. Remove the lemon zest.
10. Cover it and refrigerate it.
11. It can keep for up to a week in the fridge.