In a food processor, pulse pecans, flour, granulated sugar, cinnamon, and salt until mixture resembles coarse meal; add butter and pulse until a dough forms. Shape dough into a disk, and wrap tightly in plastic; refrigerate until firm, 30 to 60 minutes.
Preheat oven to 325 degrees. Pinch off and roll dough into balls, each equal to 1 level tablespoon. Space 1 1/2 inches apart on two large baking sheets. Bake, switching sheets from top to bottom halfway through, until cookies are just golden around edges, 20 to 25 minutes.
Cool 5 minutes on sheets; transfer to a rack to cool completely. Place confectioners' sugar in a bowl. Roll cookies in sugar twice to coat thoroughly, tapping off excess.