Special equipment: a kitchen blowtorch
Slice the orange in half and blot dry with a paper towel. Rub each half with the butter and sprinkle with the sugar. Torch with a kitchen blowtorch until caramelized. Serve with a sharp spoon, such as a grapefruit spoon.
Propane gas torches are highly flammable and should be kept away from heat, open flame and prolonged exposure to sunlight. They should be used only in well-ventilated areas. Follow torch manufacturer's instructions for use.