Place the strawberries in the bowl of a Thermomix and set to Varoma, 10 minutes, speed 2.
Add the sugar and lemon juice and cook a further 15-20 minutes, Varoma, speet 2 with the steamer basket on top of the lid.
Test for doneness. If not set, cook a further 5 minutes and check again.
Pour the hot jam into freshly sterilised warm glass jars & turn the jars upside down to cool.
Notes
To test for doneness: Place a plate in the freezer until chilled. Spoon a blob of jam in the middle and run your finger through it pressing the plate. If the two sides stay separated then it's done, if not, cook another 5 minutes and try again.