Begin by gathering all the ingredients needed for your Raspberry Swirl Shortbread Cookies. Ensure that the unsalted butter is at room temperature for easy mixing. Pre-measure the granulated sugar, all-purpose flour, egg yolk, vanilla extract, salt, and raspberry preserves to streamline the process.

In a large mixing bowl, cream together the room temperature butter and granulated sugar using a hand mixer for about 2-3 minutes until light and fluffy. Next, add the egg yolk and vanilla extract, mixing until well combined.

Gradually incorporate the flour and salt until the dough comes together and forms a soft, cohesive mass without overmixing.

Take your raspberry preserves and gently swirl them into the dough using a spatula. Be careful not to fully mix them in; the goal is to create marbled swirls.

Transfer your dough mixture onto a clean surface and divide it into two equal portions. Roll each portion into a log about 1-2 inches in diameter. Wrap each log tightly in plastic wrap and chill them in the refrigerator for at least 30 minutes.

While the dough is chilling, preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.

Once the dough has chilled, unwrap the logs and slice them into rounds, about 1/4 to 1/2 inch thick. Place the slices on the prepared baking sheet, spaced about 2 inches apart.

Bake in the preheated oven for 15-17 minutes, or until the edges are lightly golden.

After baking, allow the cookies to cool on the baking sheet for about 5 minutes before transferring them to wire racks to cool completely.