Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, baking powder, and salt, stirring with a whisk.
Combine brown sugar and butter in a bowl, and beat with a mixer at high speed until light and fluffy. Add the vanilla extract and egg white, and beat for 1 minute. Stir in the flour mixture and chopped pecans. Refrigerate the dough for 30 minutes.
Preheat oven to 350°.
Place 1/4 cup powdered sugar in a small bowl. With moist hands, shape dough into 30 (1/2-inch) balls. Roll balls in 1/4 cup powdered sugar. Place 2 inches apart on baking sheets coated with cooking spray. Place pans in freezer for 10 minutes.
Bake at 350° for 12 minutes or until cookies are golden. Cool on pans 2 minutes. Remove from pans; cool completely on wire racks. Using a fine sieve, sprinkle the remaining powdered sugar over the cookies.