Preheat oven to 375 degrees. Coat a 9 inch pie pan with butter. Mix hash and 1 beaten egg together. Press into prepared pie pan to form crust. Bake at 375 for 10 minutes. Saute onions in 3 tablespoons of butter. Layer cheese, onions and vegetables in crust. Beat together remaining eggs, evaporated milk, flour, mustard, garlic and pepper. Pour over mixture in crust. Bake at 350 degrees for 30 to 40 minutes until filling is set. Let stand for 10 minutes before serving.