Carefully wash the plums and cut them into quarters. Place the quarters into a large heat-resistant bowl (still with skins and seeds.)
Add the sugar to the bowl as well and cover it with a lid (or wrap it with cling film). Then heat it for 5 minutes in the microwave.
Take it out and stir it. Then remove the lid (or cling film) and heat it in the microwave for a further 10 minutes.
Remove the seeds and mix in the lemon juice. It's done Transfer the jam to a sterilised jar, leave it to cool, then place it in the refrigerator to store.
Story Behind this Recipe
Whenever I've looked for a plum jam recipe they all describe countless hours of simmering in a saucepan. I'm too impatient for that so I tried using the method that I usually use to make strawberry jam to make a plum version and it turned it really well.
Caution Please use a large, deep bowl as the jam has a tendency to bubble and spill over during cooking! You should be able to take any seeds out with ease after cooking.