Preheat oven to 275 degrees F (135 degrees C). Grease a baking sheet or line it with parchment paper.
Whisk sugar, flour, and salt; set aside.
In separate bowl, beat egg white until stiff. Fold sugar mixture into stiffened egg white. Add pecans and vanilla. Stir gently.
Drop by teaspoonfuls onto prepared baking sheet. Bake in preheated oven until browned, 25 to 30 minutes. Cool 5 minutes on baking sheet, then remove to wire rack to cool completely.
