Rinse the blueberries clean and pat dried with paper towels.
In a small saucepan over medium heat, add blueberries, sugar, lemon zest, lemon juice, thyme and salt. Bring to a boil and stir. Reduce heat to medium-low, cook for about 30 minutes, stirring occasionally. It may still look runny, but it will thicken more as it cools. Transfer to a clean glass jar. Cover and chill in the fridge for at least 3 hours.
Notes
When I made this jam, my blueberries were on the tart side, 1 cup of sugar seems to work great. You can use less if your blueberries are sweet.
I used quite a lot of thyme in here. You can reduce to ¾ teaspoon if you want a milder thyme flavor.
Make sure thyme is minced finely, so no big piece in the jam.
This jam can be keep for a few weeks in the fridge.