Step 1

Add the rhubarb, strawberries, sugar, cornstarch, salt, and lemon juice to a heavy-bottomed saucepan or Dutch oven.

Step 2

Mix well and cook over medium heat for 5-10 minutes. Stir often as this mixture can burn if left unattended.

Step 3

Reduce the heat to simmer and continue to cook, while stirring, for another 5-10 minutes. The filling is done when the rhubarb is soft. Remove from heat and stir in the vanilla extract and butter until the latter is melted and both are incorporated.

Step 4

Allow the mixture to cool. This pie filling can be stored in the refrigerator for up to 5 days.