An otherwise nondescript Mission block is thronged with grinning grown-ups and kids doing happy dances as they make their Mitchell's selections: will it be a classic like Kahlua mocha cream or a tropical flavor like macapuno (young coconut)? The avocado and ube (purple yam) are acquired tastes, but they've been local favorites for generations – Mitchells has kept San Francisco coming back for seconds since 1953.