Use raspberry or your favorite jam for the filling.
Preheat oven to 350 degrees. Line baking sheets with Silpats or parchment paper; set aside.
In the bowl of an electric mixer fitted with the paddle attachment, beat butter and sugar on medium speed until light and fluffy, about 2 minutes. Add egg yolk, and beat to incorporate. Beat in vanilla. Reduce mixer speed to low, and gradually add flour and poppy seeds. Beat until combined and dough begins to form around paddle. Divide dough into two equal pieces. Form each piece into a disc, wrap in plastic, and refrigerate for 1 hour.
On a lightly floured surface, working with one piece at a time, roll out dough to a 1/8-inch-thickness. Use a 2 1/4-inch round cutter to cut out cookies. Transfer to prepared baking sheets. Using a 3/4-inch round cutter, cut a hole from the center of half of the cookies. Repeat with remaining dough.
Bake until light golden brown around the edges, about 12 minutes. Remove to wire racks, and cool completely. Spread about 1/2 teaspoon of jam on all solid cookies; top each with a cookie with a cutout center.