In a bowl, combine buttermilk and lemon juice, letting it sit for 5 minutes to curdle slightly.

Peel your sweet onions and trim both the tops and bottoms. Carefully make vertical cuts in the onions to create petal-like blooms.

In a separate bowl, whisk together flour, paprika, garlic powder, onion powder, cayenne, salt, and pepper until evenly mixed.

Dip each prepared onion into the buttermilk mixture, allowing any excess to drip off. Then, coat it with the flour mixture.

Set your air fryer to 380°F (190°C) and preheat for 5 minutes.

Carefully place the coated onions in the air fryer basket and lightly spray the tops with cooking spray.

Cook the onions in the air fryer for 10–12 minutes, shaking the basket halfway through.

While the onions are cooking, mix together mayonnaise, ketchup, horseradish sauce, lemon juice, and any additional seasonings in a bowl.

Once cooked to a perfect golden-brown, remove the onions and let them cool slightly. Serve warm with your prepared dipping sauce.