Remove the stems, then cut the strawberries roughly. Put them in saucepan, you can crush them with a potato masher, if you like.
Add the sugar and lemon juice.
Heat gently, stirring with a wooden spoon until the sugar has dissolved.
Bring to the boil and cook for about 10 minutes, until it’s thick and sticky. (You could test the jam, if you like, by putting a drop of jam on a chilled plate and placing it in the fridge for 30 seconds. Then run your finger through it; if tacky it’s ready; if not, cook for another couple of minutes and retest.) Mix in the vanilla.
Transfer the spread into jars and seal with the lid. When completely cool, refrigerate.