Peel the onion but keep it whole, then slice off the top and bottom so it sits easily on its end. To get it to bloom, you need to cut slices into it as far down as possible but not all the way through, I find 4 cuts (making 8 segments) works well.
Soak the onions for 4 hours in salt water, this helps take the harsh tang from them and starts to blooming process.
Preheat your air fryer to 180 degrees C.
Place the potatoes in the air fryer, drizzle with a little olive oil then add a dollop of butter to the top of each.
Cook in your air fryer for 30 minutes, the outside may get dark, but this layer can be removed to serve.
This recipe works really well also if you roast them.