Prepare Buttermilk: In a small bowl, combine buttermilk or milk with lemon juice and let it sit for about 5 minutes until it thickens slightly.

Prep Onions: Peel and carefully trim tops and bottoms of the sweet onions and cut vertical slits down each, creating petal-like blooms.

Mix Dry Ingredients: In a mixing bowl, combine flour, paprika, garlic powder, onion powder, cayenne pepper, salt, and pepper.

Coat Onions: Dip each onion into buttermilk, then into the flour mixture, shaking off the excess.

Preheat Air Fryer: Preheat your air fryer to 380°F (190°C) for about 5 minutes.

Arrange & Cook: Place coated onions in a single layer in the air fryer basket, spray tops with cooking spray, and cook for 10-12 minutes.

Prepare Dipping Sauce: Mix mayonnaise, ketchup, horseradish sauce, and lemon juice in a bowl.

Serve Warm: Carefully remove the onions and serve them warm with the dipping sauce.