- 3/4 cup hazelnuts, toasted , any loose skins rubbed off in a kitchen towel, and cooled
- 1 cup confectioners sugar
- 1 stick (1/2 cup) unsalted butter, well softened
- 1/4 teaspoon finely grated fresh lemon zest
- 1/8 teaspoon salt
- 1 cup cake flour (not self-rising)
- 3 oz fine-quality bittersweet chocolate (not unsweetened; preferably 70% cacao), chopped
- Special equipment: parchment paper
- Put oven rack in middle position and preheat oven to 350°F. Line 2 or 3 baking sheets with parchment paper.
- Grind nuts with confectioners sugar in a food processor until powdery (be careful not to process to a paste).
- Beat together butter, zest, salt, and nut mixture in a large bowl with a rubber spatula or wooden spoon until creamy, then add flour, stirring until just incorporated (do not overwork).
- Roll level 1/2 teaspoons of dough into tiny balls (the size of marbles) and arrange 1 inch apart on baking sheets. Bake, 1 sheet at a time, until very pale golden, 12 to 14 minutes, then slide parchment with cookies onto a rack to cool completely.
- Melt chocolate in a metal bowl set over a saucepan of barely simmering water, stirring occasionally, until smooth. Spoon melted chocolate into a small plastic bag and seal bag, forcing out excess air. Snip off 1 bottom corner of bag with scissors to form a small hole.
- Pipe a small mound (about 1/8 teaspoon) of melted chocolate onto flat sides of 10 cookies, then top with 10 more cookies, pressing flat sides together to help adhere. Repeat procedure with remaining cookies.