Place the blueberries, white sugar and lemon juice in a large saucepan.
Heat, on medium heat until the fruit starts to warm up and the sugar starts to melt.
Take a potato masher and mash the blueberries to the consistency that you want.
When the sugar has melted, turn up the heat and bring to a rolling boil.
Boil, for 15 minutes while stirring to prevent it from burning on the bottom of the saucepan.
If you have a candy thermometer, it needs to read 105°C (220°F), though you will need to keep a close eye on the mixture when it starts getting around this temperature.
If you don’t have a thermometer, you can use the jam / cold plate test. Before starting your jam, simply place 3 or 4 small plates in the freezer. When you think the jam may be ready, place a small teaspoon amount of jam onto one of the cold plates from the freezer and let it sit for about 30 seconds. Then run your finger through the middle of the blob of jam. If the line starts to fill back over, it means the jam is too runny and is not ready yet, so keep cooking and repeat again in about five minutes. If the line remains, then the jam has reached setting point and is ready.
Fill your sterilised jars with the jam and seal them while they are still warm.
Nutritional information is an estimate and provided as a courtesy. The values may vary according to the ingredients and tools that are used. Please use your preferred nutritional calculator for more detailed information.