Thumbprints With Dulce de Leche, Nutella or Jam

Preparation

1. Step 1

   Heat oven to 350 degrees. Spread the hazelnuts or pecans out on a small baking sheet and cook in oven, shaking several times, until toasted, 10 to 12 minutes. If using hazelnuts, transfer to a bowl to cool, cover with a folded dish towel, then rub off the skins. (No need to toast the pistachios.)

2. Step 2

   Once cooled, transfer the nuts to a food processor, preferably a mini one. Add 2 teaspoons flour and pulse just until nuts are finely ground, being careful not to overprocess.

3. Step 3

   In the bowl of a stand mixer fitted with the paddle attachment, cream together butter and granulated sugar on medium-high speed until light and fluffy, 2 to 3 minutes, scraping bowl as needed. Add egg yolks and vanilla, and beat on medium-high speed until well combined, about 2 minutes, scraping the bowl a few times as needed.

4. Step 4

   Add ½ cup ground nuts, the salt and the remaining 2¼ cups flour; beat on low speed just until combined, then increase speed and beat until dough starts to clump together. Scrape the bowl and fold a few times to make sure everything is well mixed. Wrap dough in plastic wrap, flatten into a disk, and chill until firm, at least 1 hour and up to 3 days.

5. Step 5

   Heat oven to 350 degrees. Pinch off small pieces of dough the size of a rounded tablespoon (about 20 grams each) and roll the top half of each one in the remaining ground nuts. Place a few inches apart on parchment- or silicone mat-lined baking sheets. Chill in the freezer until firm, about 10 minutes.

6. Step 6

   Bake for 8 minutes, remove from oven and make a thumbprint in each cookie. Bake until golden brown on the bottom, and nuts are looking toasty but not burned, 6 to 8 minutes longer. Let cool a few minutes on the baking sheets and transfer to wire racks to cool further. While the cookies are still a little warm, fill each one with about ½ teaspoon of filling, and cool completely. Sprinkle with flaky sea salt. Cookies will keep in an airtight container at room temperature for up to 1 week.