In a medium saucepan, add the diced strawberries and sugar. Mix to combine and bring to a soft boil. Once boiling, add your lemon juice.
Turn down the heat and simmer for 30 minutes, or until the sauce coats the back of a spoon. Stir regularly so the strawberries don't burn or stick to the bottom of the pan. Your jam will be done when it reaches 220F on an instant read thermometer.
Remove from heat and allow to cool.
You can mash your strawberries or leave them alone, depending on the consistency you want.
Place the cooled jam in a pint sized jar. Enjoy immediately or cover with a lid and store in the refrigerator.
This recipe will make 1 pint of strawberry jam. You can easily double or triple the recipe.
You can tell when your jam is done cooking when it reaches 220F on an instant-read thermometer. Don't be off-put if your jam seems too liquidy as it can take up to 48 hours for it to fully set in the refrigerator. It's best to clip a sugar thermometer to the side of your pot as the jam boils or to use an instant-read thermometer to test the temperature before taking the mixture off of the heat.