Place a saucer in the freezer to chill.
Prepare the strawberries by removing and discarding any leaves and stalks, then cut them in to small chunks. Weigh the prepared strawberries to determine the amount of sugar you'll need. For each gram of fruit use 0.875g of sugar. My prepared fruit weighed 750g, so I'm using 656g of sugar for this batch.Example calculation: 750 x 0.875 = 656 Place the prepared strawberries and lemon juice into a tall-sided frying pan (roughly 30cm diameter is good), and cook over a medium heat until soft. Takes about 5 minutes.
Once the fruit is cooked, add the sugar to the frying pan. Stir in, turn up the heat and bring to a boil. Once boiling, immediately reduce the heat to a steady simmer and cook - with regular stirring - for 5 minutes. Remove from the heat and test the jam by dropping a little on the cold saucer. Leave for 30 seconds, then run your finger through the drop. If it wrinkles and feels tacky - it’s ready and you can proceed to the next step. If not, return to the heat and cook for 1 minute more, then remove from the heat and do the wrinkle test again. Repeat until ready.
When the jam is ready, skim off and discard any foam that has formed, then set it aside to cool for 10 minutes before spooning in to well cleaned jars. Allow these to fully cool and set. While cooling you can loosely cover the jars with a cloth if needed, but don't put lids on or refrigerate until completely cool.