Place 3 small plates in the freezer to use later for testing the jam.
Combine the fruit, sugar and lemon juice in a non-reactive heavy bottomed saucepan over medium heat. Mash the fruit with a potato masher or large fork to help break it down.
Once the sugar has dissolved, turn the heat up to high and cook until thickened, stirring frequently, about 15-20 minutes.
To check for doneness, drop a small amount of jam onto a small frozen plate. Let cool for a moment, then run a spoon or finger through the jam. If you can draw a line with clean edges that don't drip, then it is ready. If it runs back together, then cook for a few more minutes.
Turn off the heat and transfer the jam into 2 clean 8-ounce mason jars. Cool the mixture, then store in the refrigerator for up to 3 weeks.
Video
Notes
Tip: Don't skip the plate testing. To make sure your jam has the right consistency, you really don't want to skip this step!