5cupsrhubarb(about 3 large stalks, cut into 1⁄2" cubes)
2cupshulled and halved strawberries(about 1 pint)
1tablespoonfresh lemon juice(from about half of a large lemon)
Combine all ingredients in a medium to large saucepan over medium heat. Once mixture starts to bubble, reduce heat to medium low. You'll want the heat set to the point where it continues to bubble but not violently when stirred (you'll understand once you start cooking if jam bubbles start to pop out of the center of the pot). Continue to cook, stirring occasionally, until the jam has thickened. Plan on cooking jam for about an hour and temperature of the mixture is over 220°F.
While the jam is cooking, sterilize four 1-cup jelly glass jars plus their rings and lids. I do this by boiling them in water for 10 minutes or I boil the lids and run the rings and glass jars through the dishwasher.
Transfer sterilized jars, lids, and bands to a clean dish towel.
Have a very large covered pot of boiling water ready. There needs to be enough water in the pot so that when the filled jars are submerged, they're covered by at least 1" of water.
Fill each jar with hot jam, leaving at least 1⁄4" of space at the top. Place lids on jars, and secure ring bands. Secure just tight enough so that they are hand tightened but you can easily unscrew.
Transfer filled jars to pot of gently boiling water and let boil for 10 minutes. Transfer jars, set at least 1" apart, to a dish towel and let cool, undisturbed, for 24 hours. You should hear the seals on the lids pop pretty soon after removing from the water.
If any jar is not fully sealed, or you chose to skip the canning process, jam should be refrigerated and used within 2 weeks. Sealed jars will keep, in a cool, dark place, for up to a year.
Makes about 4 cups. Serving size based on 2 tablespoons.