In a small saucepan, heat the raspberry jam and lemon juice over low heat, stirring occasionally, until smooth and slightly runny. Remove from heat and let cool completely.

In a large mixing bowl, cream together the softened butter and granulated sugar using an electric mixer until light and fluffy.

Mix in the vanilla extract until fully incorporated.

Gradually add the flour and salt to the butter mixture, mixing on low speed until a soft dough forms. Be careful not to overmix.

Divide the dough into two equal portions. Flatten one portion slightly on a piece of parchment paper and spread half of the cooled raspberry jam evenly over it.

Place the second dough portion on top of the jam layer and spread the remaining jam over it.

Gently fold the dough to create swirls, being careful not to overmix. The goal is to achieve a marbled effect.

Roll the swirled dough into a log shape, wrap it tightly in plastic wrap, and refrigerate for at least 1 hour to firm up.

Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

Slice the chilled dough log into ¼-inch thick rounds using a sharp knife. Place the slices on the prepared baking sheet, leaving space between each cookie.

Bake for 10–12 minutes, or until the edges are lightly golden. Avoid overbaking to maintain the cookies' tender texture.

Allow the cookies to cool completely on a wire rack before serving or storing.