Line two baking sheets with parchment paper. Set aside.

Very finely chop the nuts. Set aside. (You should have about 1 cup.)

Place the butter, powdered sugar, vanilla, and salt in the bowl of a stand mixer. Beat with the paddle attachment on low speed to blend, then beat on medium speed until smooth and creamy. Add the flour and continue beating on low speed until a stiff dough forms, scraping down the sides of the bowl as needed. Add chopped nuts and mix for a few seconds longer to incorporate them into the dough.

Divide the dough into 32 balls, using about 1 tablespoon for each, and arrange them on one of the prepared baking sheets.

To create the Nutella centers, flatten a dough ball in your palm into a 1/2-inch-thick disk. Spoon a scant teaspoon of cold Nutella into the center of the disk and enclose the dough around it. Gently roll the dough back into a smooth ball. Return ball to the baking sheet and repeat with the remaining dough and Nutella.

Transfer baking sheet to the freezer for 15-20 minutes for dough to firm up.

Preheat the oven to 350°F.

Remove the baking sheet from freezer. Transfer half the cookies to the second baking sheet and arrange so they're spaced about 1 inch apart.

Bake the cookies on racks in upper third and lower third of oven for 8 minutes. Switch pan positions, then continue baking until light golden at the bottom edges, 6-8 minutes.

Check to see that cookies are done. Remove from oven or add time as needed.

Let cookies cool on the pans for 5 minutes.

Place the powdered sugar in a large bowl. Roll the warm cookies in the powdered sugar, then transfer to cooling racks. The sugar will appear to melt into the cookies.

Let the cookies cool completely, at least 1 hour. Roll once more in powdered sugar. This time, the sugar will remain on the cookies’ surface.

Serve the cookies immediately, or store in an airtight container at room temperature for up to three days, or in the refrigerator for five days. Bring to room temperature before serving.