Prepare the Raspberry Swirl

1. Cook the Raspberry Puree: In a small saucepan, combine the raspberries, sugar, and lemon juice. Heat over medium heat, stirring occasionally until the raspberries break down and the mixture thickens, about 5-7 minutes. Remove from heat and let it cool to room temperature.

Make the Shortbread Dough

1. Preheat the Oven: Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.
2. Mix the Butter and Sugar: In a large bowl, beat the softened butter and powdered sugar together until light and fluffy. This will take about 3-4 minutes with an electric mixer.
3. Add Vanilla: Stir in the vanilla extract, making sure it’s fully incorporated.
4. Add Dry Ingredients: Gradually mix in the flour and salt, a little at a time, until the dough comes together. It should be slightly crumbly but hold its shape when pressed.
5. Chill the Dough: Divide the dough into two portions, wrap them in plastic wrap, and chill in the refrigerator for 30 minutes. Chilling helps the dough hold its shape while baking.

Assemble the Cookies

1. Roll the Dough: On a lightly floured surface, roll out one portion of dough to about 1/4-inch thick. If it’s too soft, you can refrigerate it again to make it easier to work with.
2. Add the Raspberry Swirl: Spoon small dots of the cooled raspberry puree onto the dough. Use a toothpick or a skewer to gently swirl the raspberry into the dough. Be careful not to overdo it—you want the swirl to remain distinct.
3. Cut the Cookies: Use a cookie cutter or knife to cut the dough into desired shapes (round, square, or even heart-shaped for a more festive look).
4. Bake: Place the shaped cookies on the prepared baking sheets, spacing them about 1 inch apart. Bake in the preheated oven for 12-15 minutes, or until the edges are lightly golden.
5. Cool: Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.