1. Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.
2. In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy. This usually takes about 3-4 minutes with a hand mixer or stand mixer.
3. Beat in the egg and vanilla extract until fully incorporated.
4. In a separate bowl, whisk together the flour, baking powder, and salt.
5. Gradually add the dry ingredients to the wet, mixing just until combined. If the dough feels too stiff, add a tablespoon of milk to bring it together.
6. Divide the dough in half. Roll out one half between two sheets of parchment paper into a rough rectangle about ¼ inch thick.
7. Spread small spoonfuls of jam evenly over the rolled dough, leaving a ½-inch border around the edges.
8. Roll out the second half of the dough to the same size and place it gently over the jam-covered dough.
9. Press down lightly, then use a knife or pizza cutter to trim the edges and cut the dough into individual cookie rectangles, about 3×2 inches each.
10. Transfer the cookies to the baking sheets (use a spatula if needed) and prick a few holes in each with a fork to allow steam to escape.
11. Bake for 12-15 minutes, or until the edges turn golden and the tops are set.
12. Allow the cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

One personal trick I learned from my years in restaurant kitchens is not to rush the cooling process. These cookies firm up beautifully once cooled, and that’s when the layers truly shine.