In small skillet over medium heat, cook celery, pepper, and onion in butter until tender but not brown, about 6 minutes. Sprinkle vegetables, ham, and cheese into pie shell. Beat together eggs, milk, salt, if desired, and paprika until well blended. Pour over vegetable mixture.
Bake preheated 375° F oven until knife inserted near center comes out clean, about 30 to 40 minutes. Let stand 5 minutes before serving.
Garnish with onion rings and onion curls, if desiredServings: 2 to 4