In a large bowl, whisk together the sour cream, the milk and the hot sauce. Add the onion rings and set aside while you season the flour. In a large baking dish or pie plate, combine the celery salt, onion powder, garlic powder, mustard powder, paprika, chili powder, white pepper, salt and the flour.
Heat about 3 inches of oil to 350 degrees F in a large Dutch oven.
Remove the onion rings from the liquid mixture and dredge in the flour mixture. Repeat the process to double coat the rings. Place the onion rings into the oil in batches and fry until golden brown and crispy, about 5 minutes. Drain the onion rings on a paper towel lined plate and season with salt while still hot, then transfer to a serving platter. Serve with the Crab Burger and Celery Root Remoulade.