Prepare half-pint jars by boiling the lids, rings and jars in boiling water for 5 minutes. This is known as the water bath method.
Slice the strawberries into small chunks. You could also use a potato masher to reduce the size of the fresh berries.
Cut the rhubarb into small chunks, approximately half an inch in size.
Next,in mixing bowl combine the chopped strawberries, rhubarb, and sugar. Give it a good mix and let it sit for about an hour. This allows the flavors to mingle and develop.
After the hour is up, transfer the fruity mixture to a wide saucepan, large pot, or skillet. Keep stirring constantly as you cook it over medium heat until it starts gently boiling. While cooking, you might notice some foam forming on the surface; simply scoop it out with a spatula.
Continue cooking and stirring until the mixture thickens. It's crucial to stir constantly to avoid burning the jam, and it also helps to prevent any splattering. This process will likely take around 20 minutes or more. 5 minutes before the end of cooking stir in the lemon juice.
To check if the jam is ready, use a spoon to create an open trail behind it as you stir. Once the mixture reaches this thickness, you'll know it's done. (See pictures in the blog post)
Remove the saucepan from the heat and allow the jam to cool completely before serving.
Now, it's time to enjoy your homemade jam!