Make the Dough
In a large bowl, cream together butter and granulated sugar until light and fluffy (about 2–3 minutes). Add egg yolks and vanilla extract, mixing until smooth.
Add Dry Ingredients
In a separate bowl, whisk together flour, ground almonds (or hazelnuts), cinnamon, and salt. Gradually add to the butter mixture, mixing just until combined. Dough should be soft but not sticky.
Chill the Dough
Divide dough in half, flatten into discs, and wrap in plastic wrap. Refrigerate for at least 1 hour (this makes rolling easier and prevents spreading).
Preheat Oven
Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.
Roll & Cut Cookies
On a lightly floured surface, roll dough to about ¼-inch thickness. Use a round cookie cutter to cut out base cookies. For the tops, cut out the same size round, then use a smaller star or heart cutter to create a “window” in the center.
Bake the Cookies
Place cookies on prepared baking sheets and bake for 8–10 minutes, or until edges are lightly golden. The cookies should remain pale on top. Let cool on baking sheet for 5 minutes, then transfer to a wire rack.
Assemble Sandwiches
Spread about 1 teaspoon of raspberry jam on the bottom (solid) cookies. Dust the “window” tops with powdered sugar, then gently place them on top of the jam layer to form a sandwich.
Serve & Store
Enjoy immediately, or store in an airtight container at room temperature for up to 5 days. The flavor deepens after a day as the jam softens the cookie slightly.