Cover the frozen frog legs with cold milk and defrost them in it leisurely (!) in 1-2 hours.
Take them out, dry them carefully with kitchen paper and turn them in flour on the other side.
In a griddle or possibly frying pan, heat the butter and roast the frog legs in 10-15 min over medium heat, turning frequently, until crispy on both sides.
In the meantime, chop the garlic and parsley. Arrange the frog legs on a heated serving platter and sprinkle with garlic, salt, pepper and parsley. Serve with a wedge of lemon.