Add strawberries and sugar to a large saucepan and bring to a medium heat. Stir constantly until the sugar has dissolved (at this point you can mash the fruit with a potato masher or a spoon).
Once the sugar has fully dissolved, increase the heat to a medium high temperature and bring to the boil. Boil for about 5 - 10 minutes, until the jam has reached 105˚C on a preserving thermometer***
Once ready, pour the hot jam into sterilised jars using a metal funnel, and seal with sterilised lids (we sterilise ours by placing them into the oven and heating them up in the oven beforehand****)
* About 445 ml
** If using frozen strawberries, make sure to defrost them before use. Learn from my mistakes!
*** If you don't have a thermometer, to see if the jam is ready, while it is still on the boil, use a teaspoon to place a bit onto a small plate. Leave it for about 30 seconds, then push the jam with your finger. If it doesn’t flood to fill the gap it's ready. If not, keep it on the boil and repeat this step after every minute or so, until it has set.
**** Pouring hot jams into cold jars will cause the jars to crack/smash, if you want to pour the jam into cool jars, bring the jars and the jam down to room temperature.