Add all ingredients into a small pot on medium heat, stir while you allow the berries to defrost.
Once the berries are defrosted, use a potato masher to begin smashing the blueberries. Once all the blueberries are pressed, the mixture will have a ton of liquid. Bring the mixture to a boil on high, then lower the heat to medium-low to simmer.
Continue stirring for 5-10 minutes until the liquid is mostly absorbed and the mixture is thickened. If the mixture starts to burn, turn down the heat to low. The mixture should resemble a semi runny jam-like texture when done. You can eat it now, but most people prefer it chilled. It will also gel up further as it cools.
Remove from heat and place in a mason jar or other jam container and place the container in the fridge for at least 2 hours.
Notes
The recipe is not preserved, so it stays good for 5-10 days in the fridge. I have not tried freezing it. If you do, let me know how it goes! More lemon juice helps with preservation but obviously alters the taste.