In a medium saucepan, combine the chopped strawberries, rhubarb, sugar, and lemon juice. Cook over medium-low heat, stirring occasionally, until the sugar dissolves and the fruit breaks down, about 5 to 10 minutes. Remove from heat and set aside to cool.

Preheat your oven to 350°F. Line a baking sheet with parchment paper and set aside.

In a large bowl, use an electric mixer to beat the softened butter and powdered sugar together until smooth and creamy, about 1 to 2 minutes.

Add the vanilla extract and mix until combined.

Gradually add the flour and mix until a soft dough forms. You may need to use your hands to bring it together.

Using a 1 1/2-tablespoon scoop, portion the dough onto the prepared baking sheet, spacing them about 2 inches apart.

Working with one portion at a time, roll it into a smooth ball. Use the back of a rounded measuring spoon or your thumb to create an indentation in the center, being careful not to press all the way through.

Repeat with the remaining dough portions.

Fill each indentation with about 1/2 to 1 teaspoon of the cooled strawberry rhubarb jam, depending on the depth of the indent.

Bake for 18 to 20 minutes, or until the cookies are set and the edges are lightly golden. Let cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.