Beat butter and 3/4 cup powdered sugar at medium speed with an electric mixer until creamy. Stir in vanilla and pecans. Gradually add flour; beating until a soft dough forms. Cover and chill one hour.
Divide dough into 5 portions; divide each portion into 12 pieces. Roll dough pieces into 2-inch logs, curving ends to form crescents. Place on ungreased baking sheets.
Bake at 350° for 10 to 12 minutes, or until lightly golden. Cool on baking sheets 5 minutes. Roll warm cookies in 2 cups powdered sugar. Cool completely on wire racks. Roll cookies in remaining powdered sugar. Makes about 5 dozen.