To keep the shells from being tough, spoon the flour into the measuring cup instead of packing it. Use large eggs, and spread the mixture thinly into the muffin cups. Baked shells may be frozen for later use.
Combine first 5 ingredients in a bowl; stir well. Spoon mixture evenly into 12 muffin cups coated with cooking spray, pressing mixture into bottom and up sides of muffin cups. Bake at 400° for 15 minutes or until edges are browned. (Do not overbake.) Cool 2 minutes in pan on a wire rack. Remove from pan; cool completely on wire rack.