Cream together butter and sugar until light and fluffy, then beat in egg yolk and vanilla extract.

Gradually add flour and salt, mixing until just combined to form a soft dough, then flatten into a disc, wrap, and chill for at least 30 minutes.

Preheat oven to 350°F (175°C) and roll out the chilled dough on a lightly floured surface to about 1/8-inch thickness.

Cut out 10 rounds using a cookie cutter, creating a small window in the center of 5 of the rounds, and place them on a baking sheet lined with parchment paper.

Bake for 10-12 minutes, or until the edges are lightly golden, then transfer to a wire rack to cool completely.

Once cooled, dust the cookies with the cut-out centers with powdered sugar.

Spread a small amount of raspberry jam on the flat side of the remaining 5 cookies and gently top each with a powdered sugar-dusted cookie to create a sandwich.