Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper.

In a bowl, whisk together the gluten-free flour, baking powder, and salt. Set aside.

In another bowl, cream together the softened butter and granulated sugar until light and fluffy.

Add the egg yolk (reserve the egg white for later) and vanilla extract to the butter-sugar mixture, beating until well combined.

Gradually add the dry ingredients to the wet ingredients, mixing until a dough forms.

Shape the dough into tablespoon-sized balls and place them on the prepared baking sheets, spacing them a few inches apart.

Use your thumb or the back of a spoon to create an indentation in the center of each cookie.

In a small bowl, lightly beat the reserved egg white. Brush the edges of each cookie with the egg white.

Fill each indentation with a small amount of jam or preserves.

Bake the cookies in the preheated oven for 10-12 minutes or until the edges are lightly golden.

Remove the cookies from the oven and let them cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.