Put the cleaned strawberries in a big pot. Add the sugar and lemon juice and mix well.
Keep them in the fridge to macerate overnight.
The next day, take the pot out of the fridge and put it onto the stove.
Stir well and cook over moderate to high heat, stirring often so it does not stick to the bottom of the pan, for about 40 minutes.
After the first 20 minutes have passed you can blend the strawberries with a stick mixer – this is optional – do it only if you like your jam smoother (without fruit pieces in it).
While it’s cooking, put a small plate in the freezer.
Once the bubbles subside and the jam appears like it is beginning to gel, put the fire off.
Put a small amount of jam on the frozen plate and return it to the freezer for a few minutes. If it wrinkles when you nudge it, it’s ready. If not, cook it some more and test it again until it’s ready.