In a large cast-iron or other heavy skillet, saute onions and red peppers in butter until tender. Add 1/4 cup garlic, celery salt and pepper; cook 1 minute longer.
Transfer to a large bowl. Add the potatoes, cheeses, flour, sour cream and remaining garlic; mix well.
Heat 1/4 in. of oil in same skillet over medium heat. Working in batches, drop batter by 1/4 cupfuls into hot oil. Press lightly to flatten. Fry until golden brown, carefully turning once. Drain on paper towels. Sprinkle with parsley.