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

Heat over medium heat until the mixture begins to bubble.

Reduce heat to medium-low and simmer gently.

Stir occasionally to prevent sticking.

Cook for about 1 hour until thickened and temperature reaches 220°F (104°C).

Remove from heat and allow to cool slightly.

For storage:

Transfer to clean jars for refrigeration or freezing.

For canning, follow proper sterilization and water bath method.

This strawberry rhubarb jam thickens as it cools and develops even deeper flavor.