Wash and prepare the rhubarb by chopping it into small pieces. Hull and chop the strawberries.

In a large saucepan, combine the rhubarb, strawberries, sugar, and lemon juice.

Heat the mixture over medium heat, stirring frequently, until the sugar dissolves and the fruit begins to break down, about 10 minutes.

Bring the mixture to a gentle boil, then reduce the heat to a simmer and cook for 20-25 minutes, stirring occasionally, until the jam thickens.

To test the jam's readiness, place a small spoonful on a chilled plate. If it holds its shape and wrinkles slightly when pushed, it’s ready. If not, continue cooking and testing every few minutes.

Once the jam is ready, remove it from heat and let it cool slightly.

Carefully transfer the jam to sterilized jars, leaving a small amount of headspace at the top. Seal the jars tightly.

Allow the jam to cool completely before refrigerating or storing in a cool, dark place.