Follow the steps in order for the best result.
Begin by stirring the softened butter until it reaches a smooth consistency. Incorporate the sugar and beat until the mixture is light and fluffy.
Introduce the egg and vanilla extract, ensuring they are thoroughly combined through vigorous beating.
In a separate mixing bowl, whisk together the flour, baking powder, and salt to ensure even distribution.
Gradually add the dry ingredients to the creamed mixture, beating until just combined. Be careful not to overmix.
Shape the resulting dough into a cohesive ball. Envelop it in plastic wrap and refrigerate for a minimum of 2 hours to allow the gluten to relax and the flavors to meld.
In the meantime, prepare the raspberry filling by combining all the filling ingredients in a bowl. Mix well.
On a lightly floured sheet of wax paper, roll out the chilled dough into a 12x9 inch rectangle.
Evenly spread the raspberry filling over the dough, leaving a 1/2-inch border along the edges.
Carefully roll the dough into a jellyroll shape, starting from the long end. Gently peel away the wax paper as you roll to prevent sticking.
Pinch the side seam to seal the roll securely, leaving the ends open. Wrap the log in plastic wrap and chill for an additional hour.
Preheat your oven to 375°F (190°C).
Unwrap the chilled dough log and slice it into 1/4-inch thick rounds.
Arrange the cookie slices on greased baking sheets, spacing them approximately 2 inches apart to allow for spreading.
Bake for 8-10 minutes, or until the edges are lightly golden brown and the cookies are just set. Keep a close eye on them to prevent over-baking.
Remove the baking sheets from the oven and allow the cookies to cool on the sheets for a few minutes before transferring them to a wire rack to cool completely.
Enjoy your homemade Raspberry Swirl Cookies with a cup of tea or coffee!