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

In a mixing bowl, cream together the softened butter and granulated sugar until light and fluffy, about 2-3 minutes.

Add the egg, vanilla extract, lemon zest, and lemon juice to the butter mixture. Mix until well combined.

In another bowl, whisk together the all-purpose flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Divide the cookie dough into two equal portions. In one portion, gently fold in the raspberry jam until fully combined, creating a raspberry dough.

To assemble the cookies, scoop a tablespoon of the lemon dough and a tablespoon of the raspberry dough. Place them together on the baking sheet and gently swirl them together with a toothpick or the back of a spoon.

Bake in the preheated oven for 10-12 minutes or until the edges are lightly golden. Allow to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

For extra flavor, consider adding a pinch of lemon extract to the cookie dough.

Store these cookies in an airtight container at room temperature for up to 5 days.