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

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

Add the egg yolk and vanilla extract, mixing until well combined.

In a separate bowl, whisk the all-purpose flour and salt together. Gradually add the flour mixture to the wet ingredients, mixing until just combined. The dough should be soft but not sticky.

Chill the dough in the refrigerator for about 30 minutes to help the cookies hold their shape while baking.

Roll out the dough on a floured surface to about 1/8-inch thick.

Use a heart-shaped cookie cutter to cut out shapes; place half of the cookies on the prepared baking sheets.

For the remaining cookies, cut out a smaller heart shape in the center of each one to create a window for the jam.

Spread a teaspoon of your chosen jam onto each whole cookie.

Place the cut-out cookies on top of the jam-covered ones to create a sandwich.

Bake in the preheated oven for 12-15 minutes, or until the edges are lightly golden.

Let the cookies cool on the baking sheets for a few minutes before transferring them to a wire rack.

Once cool, dust with powdered sugar if desired.