Heat oven to 400°F.
Unroll pie crusts. Roll each crust to 12 inches in diameter. Using 4-inch round cutter, cut 6 rounds from each crust. Firmly press each round in bottom and up side of each of 12 ungreased regular-size muffin cups. Bake 7 to 10 minutes or until lightly browned. Remove from oven. Reduce heat to 350°F.
In small microwavable bowl, microwave frozen vegetables and 2 teaspoons water tightly covered with plastic wrap on High 3 minutes; set aside.
In 8-inch nonstick skillet, heat butter over medium heat until melted and hot. Add onion to skillet; cook, stirring frequently, until onions are translucent, 3 to 5 minutes. Add beef to skillet; cook 5 to 7 minutes longer, stirring to break up any large pieces; drain. Add broth, salt and pepper. Cook 3 to 5 minutes longer or until mixture is hot and liquid is absorbed. Stir in vegetables.
Fill each muffin cup with 1/4 cup beef mixture. Top each pie with about 1/4 cup of the warm mashed potatoes. Bake at 350°F 25 to 30 minutes or until crusts are golden brown and mashed potatoes are lightly browned. Let stand 10 minutes in pan before serving. Run knife around outside of each pie to loosen before removing.