In a large skillet, melt butter and saute onions, celery and garlic for about 45 minutes or until they are cooked down.
Stir in flour and cook briefly, do not brown. Stir in chopped shrimp and cook for 20 minutes.
Pour in 1 1/2-2 cups of water or vegetable stock and mushrooms. Stir in paprika and season with salt, pepper and red pepper flakes. Cook for 30 minutes. Should be a thick and have a gravy-like consistency.