• Place rhubarb, strawberries, water and sugar in a medium-sized pot set over medium heat. Cook, stirring often, until the juices are released and begin to cover the fruit. Pour the mixture through a fine mesh sieve to separate the fruit from the juices. Set the fruit aside.
• Return the the juices to the pot and bring to a boil over medium-high heat. Allow to cook, stirring frequently, until reduced by approximately half (an easy way to check this is to use the handle of a wooden spoon. Dip it into the liquid to “stain” it. Then use that as a measuring guide for how much it’s cooking down). Skim off any foam that rises to the surface, as you go.
• Add the fruit back to the pot, along with any accumulated juices. Stir in lemon juice. Bring to a simmer and cook until a spoonful of the mixture mounds on a frozen plate without spreading. Once ready, you can pack it into jars, or tupperware, and freeze. Or, follow the process below for canning.

To can

• While jam is cooking, sterilize 5, ½ pint jars along with lids. Fill the jars to within ¼ inch of the top with jam; wipe the rims, top with lids and tighten rings to fingertip tight. Process in a boiling water bath for 5 minutes. Remove jars from water bath and set on a kitchen towel to cool for 24 hours. Check for seals (you’ll hear a pop when it seals) before storing in a cool, dark place until ready to use.