Place pecans, 1/2 cup (45 g) powdered sugar and salt in bowl of food processor fitted with metal blade. Pulse on and off to break up nuts, then process until nuts are finely ground. Add butter a few pieces at a time, pulsing on and off to incorporate, then run machine until mixture is smooth; pulse in vanilla extract. Add flour and pulse machine on and off until incorporated, scraping the dough down once or twice. Process until the dough begins to form a ball. Remove dough from machine, form into a very flat disc, wrap in plastic wrap and refrigerate at least 2 hours or until firm enough to roll into balls. Dough may be refrigerated overnight. (You may freeze dough up to 1 month; defrost in refrigerator overnight before proceeding).

Preheat oven to 350°F/180°C. Line two half-sheet baking pans with parchment paper.

Roll dough between your fingers and palms with lightly floured hands into 1-inch (2.5 cm) balls and place on prepared cookie sheets 2-inches (12 mm) apart. Gently flatten just enough so they don’t roll off the sheet.

Bake for about 15 to 20 minutes or until light golden brown around the edges and on the bottom. Take care when checking, as they are very fragile when hot.

Cool cookies on sheets placed on racks for 5 minutes, then sift about half of the remaining sugar over the warm cookies. Place remaining sugar in a small bowl. After cookies have cooled completely, roll them in the powdered sugar in the bowl to cover completely. Cookies may be stored at room temperature in an airtight container for up to 2 weeks. I recommend arranging in single layers, separated by parchment paper - and no more than 2 layers tall.