Scrub the potatoes and dry them completely. Prick each one 4–5 times with a fork. Rub with olive oil and sprinkle with 1 teaspoon kosher salt.
Place in the air fryer basket in a single layer. Air fry at 400°F for 35–40 minutes, until a knife slides into the center with no resistance.
Let cool 10 minutes, then slice each potato in half lengthwise.
Scoop the flesh into a large bowl, leaving about 1/4 inch attached to the skin so the shells hold their shape.
Mash the flesh with the butter until the butter melts in. Fold in the sour cream, 1 cup of the cheddar, the bacon, chives, 1/2 teaspoon salt, and pepper. Add milk a tablespoon at a time only if the filling seems stiff. Do not over-mix.
Mound the filling back into the shells, heaping slightly.
Air fry at 375°F for 10–12 minutes, in a single layer with space between each. Work in batches if needed.
Scatter the remaining 1/2 cup cheddar over the tops during the final 2–3 minutes and cook until melted and browned.
Serve hot with extra chives and sour cream.