Preheat the oven to 350°F. Place pecans, ½ cup powdered sugar and salt in a food processor fitted with a metal blade. Pulse on and off to break up nuts, then process until the nuts are finely ground.
Add butter a few pieces at a time, pulsing on and off to incorporate, then process until the mixture is smooth; pulse in vanilla. Add the 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 the dough from the machine and shape into a flat disc. Wrap in plastic wrap and refrigerate for at least 2 hours or until firm enough to roll into balls. Dough may be refrigerated overnight.**
Drop one tablespoon dough (I used a #50 scoop) into each cup of a greased mini muffin tin. Using the end of a thick-handled wooden spoon make a small, deep well in the center of each cookie.
Bake for 13 to 15 minutes or until light golden brown on the bottoms and around the edges. Remove from the oven and cool in the pan for 5 minutes before transferring to cooling racks to cool completely.
Sift the remaining 1 ½ cups powdered sugar over warm cookies. Immediately fill the indentations with jelly and allow to cool completely.