Preheat oven to 425 ̊.
Melt 1 tablespoon butter in a large ovenproof skillet.
Add apples, fennel, and shallots and cook until golden, 2–3 minutes.
Stir in thyme, allspice, salt, and pepper.
Roast, tossing once, until tender for 15 minutes.
Add 1 more tablespoon butter and cider vinegar; toss until glazed, for 1 minute.
Top with fennel fronds.