Combine first 4 ingredients in a large bowl; stir with a whisk. Add egg whites, 1 at a time, beating with a mixer at medium speed until combined; scrape bowl occasionally. Add vanilla, and beat well. Fold in pecans. Drop batter by level tablespoons 2 inches apart onto baking sheets coated with cooking spray.
Bake at 325° for 15 minutes or until dry on the surface and centers are soft. Remove from oven; cool on wire racks for 15 minutes or until cookies can be easily removed with a spatula. Cool completely on wire racks.