Roll each piecrust into a 12-inch square; cut each square into 24 pieces. Shape into balls, and press into lightly greased miniature muffin pans.
Melt butter in a large skillet over medium heat. Add onions and parsley; sauté until onions are tender. Add spinach; cook 2 minutes. Stir in Worcestershire sauce, salt, and pepper. Remove from heat.
Whisk together eggs and milk until blended; stir in cheese. Add egg mixture to spinach mixture; spoon evenly into prepared pans.
Bake at 350° for 30 to 35 minutes. Remove immediately from pans, and cool on wire racks. Freeze quiches up to 2 months.
Note: Thaw frozen quiches in refrigerator; bake at 300° for 10 minutes or until thoroughly heated.