Cut off the leaf and root end of the rhubarb stalk, then wash the stalk under cool water.  

Dice the rhubarb into ½” pieces to get approximately 6 cups of diced rhubarb.

Rinse the strawberries, cut off the green tops and center core if necessary, and remove any brown or soft spots.  Dice the strawberries to get approximately 3 cups.

Place the rhubarb, strawberries, sugar, and ½ cup water into a large pot.

Cook the fruit and sugar mixture until the juices cover the fruit, approximately 10-15 minutes.

Place a colander over a large bowl, and pour the fruit mixture into the colander.  Capture the drained juices in the bowl, stirring the fruit gently, allowing additional juice to flow through.

Pour the juice back into the pot, and reserve the fruit pulp for later, continuing to capture any juices that drain off.

Cook the juice over medium-high heat until boiling, stirring frequently.  Continue to boil until the juice is reduced to about 1½ cups, stirring occasionally for approximately 20 minutes.

Carefully add the retained fruit pulp from the colander, any additional captured juices, and ¼ cup of freshly squeezed lemon juice into the boiling juice.

Reduce heat to medium-high and simmer, stirring frequently.

Cook the jam until it nears the gel stage, which should take approximately 15 minutes.

Test the jam to see if it has reached the gel stage by using the cold plate test until the juices no longer run on the plate, providing a fairly firm set.

Remove the jam from the heat, skim off as much foam as possible, and gently stir the jam mixture for about a minute to ensure the fruit pulp remains distributed within the juice.

Ladle or pour the jam into prepared jars or containers.

If canning, process in a water bath canner for 10 minutes (or 15 minutes if above 6,000 feet in elevation).