Chocolate-Filled Hazelnut Cookies

Ingredients

• 3 oz bittersweet chocolate unsweetened 70% chopped (not ; preferably cacao)
• 1 cup cake flour (not self-rising)
• 1 cup powdered sugar 
• 0.8 cup hazelnuts cooled toasted
• 0.3 teaspoon lemon zest fresh finely grated
• 0.1 teaspoon salt 
• 0.5 cup butter unsalted softened well

Equipment

• food processor
• bowl
• baking sheet
• sauce pan
• baking paper
• oven
• wooden spoon
• ziploc bags
• spatula
• kitchen scissors

Directions

1. Put oven rack in middle position and preheat oven to 350°F. Line 2 or 3 baking sheets with parchment paper.
2. Grind nuts with confectioners sugar in a food processor until powdery (be careful not to process to a paste).
3. 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).
4. Roll level 1/2 teaspoons of dough into tiny balls (the size of marbles) and arrange 1 inch apart on baking sheets.
5. 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.
6. 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.
7. 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.
8. • Cookies can be baked and cooled, but not filled, 1 week ahead and kept in an airtight container at room temperature. • Filled cookies are best eaten the same day, but leftovers keep in an airtight container at room temperature 2 days.