Place the nuts, flour, baking powder, and salt in the bowl of a food processor fitted with the blade attachment and pulse until the nuts are finely ground. Stop immediately if a ring of moist crumbs adheres to the base edges of the bowl.

Place butter and both sugars in a large bowl and use an electric mixer to beat it until light and creamy, about 2 to 3 minutes. Scrape down the sides of the bowl, add yolks and vanilla, then beat until incorporated, about another 30 seconds.

Sprinkle ground hazelnuts and other dry ingredients over butter mixture and mix until just incorporated. Divide dough in half and wrap each in plastic wrap. Chill dough packets in the fridge for at least 1 hour and up to 2 days.

Heat oven to 350°F. Line two baking sheets with parchment paper or silicone baking mats. Roll out the first dough packet until between 1/8 and 1/4-inch thick. Use a 2-inch cutter of your choice to cut out rounds of dough. Use a smaller cookie cutter (a 3/4-inch is ideal) to remove the centers of half of the cookies, creating ring shapes that will later form the lids. If the dough becomes too soft as you’re using it, just slip it into the freezer for a few minutes so that it firms up again.

Bake cookies until golden at edges, rotating trays as needed, about 8 to 9 minutes. Cool on baking sheets for 5 minutes before transferring to a wire rack to finish cooling. Repeat with remaining dough; you can re-chill and re-roll cookie scraps.

If powdering the linzer lids, arrange the ring-shaped cookies (the ones you removed the centers of) on a baking rack with a tray or paper underneath to catch the mess. Sprinkle with powdered sugar.

Spread each of the cookie bases with about 1 teaspoon chocolate-hazelnut spread. Fit a ring-shaped lid on each. Cookies will keep at room temperature in an airtight container for several days.

To toast your hazelnuts: Hazelnuts can be toasted on a baking sheet in the oven at 350°F for 10 minutes, but don’t take them out just yet. This can take an extra 1, 2, or even 5 minutes. Check frequently. Well-toasted hazelnuts have a deeper nutty flavor, and their skins come off easily.

There are two methods to skin hazelnuts: rubbing them with a towel while warm, or letting them cool and rolling them around in your dry hands. Both methods work.