Preheat the oven to 325 degrees F. Line two baking sheets with parchment paper or a Silpat baking mat. Set aside.
Place 1 cup pecans (plain pecans) in a food processor and process for about 15 seconds or until the texture is similar to coarse cornmeal. Transfer the pecans to a medium bowl. Place the candied pecans, if using, in the food processor and process until coarsely chopped, about 10 seconds. Add the chopped pecans to the bowl with the ground pecans.
Stir the flour and salt into the pecans. Set aside.
In the bowl of a stand mixer, beat the butter and sugar at medium speed with the beater blade until fluff, about 3 minutes. Beat in the vanilla extract.
Reduce the speed to low and slowly add in the nut mixture. Mix until combined, about 30 seconds. Scrape down the bowl with a spatula and mix until the dough comes together. Give the dough a final stir by hand to mix in any remaining flour.
Roll the cookie dough into balls, about 1 tablespoon of dough per cookie. Place the balls on the prepared baking sheets, spacing them 1 inch apart.
Bake for 18 minutes or until cookies are pale golden and the bottoms are beginning to brown. Remove from the oven and let the cookies cool on the baking sheet for 5 minutes. Transfer to a cooling rack and cool completely.
Pour confectioner's sugar in a small bowl and roll the cookies in the sugar until the are well coated. Before serving, reroll cookies in sugar and gently shake off the excess sugar.
Notes-you can use just regular pecans, but I love using half candied pecans. They are SO good in these cookies. You can also use walnuts if you wish. To make super fine sugar, place the sugar in the food processor and process for about 30 seconds.