Heat oven to 350°F. Place paper baking cup in each of 24 regular-size muffin cups. In medium bowl, mix flour, baking powder and salt; set aside. In large bowl, beat shortening with electric mixer on medium speed 30 seconds. Gradually add granulated sugar, about 1/3 cup at a time, beating well after each addition. Beat 2 minutes longer. Add egg whites, one at a time, beating well after each addition. Beat in 2 1/2 teaspoons vanilla. On low speed, alternately add flour mixture, about a third at a time, and milk, about half at a time, beating just until blended.