In a small saucepan over low heat, combine raspberry jam, cornstarch, and lemon juice. Stir until smooth and slightly thickened. Let cool completely.

In a large bowl, cream together softened butter and sugar until light and fluffy. Beat in vanilla extract.

Gradually add flour and salt to the butter mixture, mixing just until combined. The dough will be soft but should hold together.

Divide dough into small balls (about 1 tablespoon each). Place on a parchment-lined baking sheet. Flatten slightly and use your thumb or the back of a spoon to make an indent in the center.

Spoon a small amount of the cooled raspberry mixture into each indent. Use a toothpick to gently swirl the jam into the dough.

Chill the tray of cookies for 15–20 minutes in the fridge while you preheat the oven to 350°F (175°C).

Bake for 12–15 minutes, or until the edges are lightly golden. Let cool on the pan for a few minutes, then transfer to a wire rack