Combine first six ingredients in a large mixing bowl; mix well. Set aside.
Divide pastry into 6 equal portions; roll each portion into a circle, 8 inches in diameter. Place 3/4 cup beef mixture on each pastry circle. Dot with 1 teaspoon butter, and sprinkle with 1 teaspoon water. Fold pastry circle in half, making edges even. Using a fork, press edges of pastry together to seal. Brush each pie with milk.
Place on baking sheets, and bake at 375° for 55 minutes or until browned. Serve warm with mustard.