Mix the shallot and vinegar together in a small bowl and set aside for at least half an hour.
Heat a heavy-based skillet until hot. Toss the asparagus and radishes in the oil in a bowl and season well. Sear the asparagus first, letting it crackle and sizzle in the pan. It should go bright green within about a minute, then turn the spears over and cook them for a further minute or so bef