Wash and drain the raspberries. Put them in saucepan, you can crush them slightly with a potato masher, if you like.
Add the sugar and lemon juice. Bring to the boil gently, stirring with a wooden spoon until the sugar has dissolved.
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 then placing it in the fridge for 30 seconds. Then run your finger through it - if tacky and wrinkled it’s good; if not, cook for another couple of minutes and retest.)
Mix in the vanilla and let it cool.
Transfer the jam into a sterilised jar and seal with the lid. Chill until needed.