Melt 2 tablespoons butter in a large ovenproof skillet. Add 2 Gala apples and 1 fennel bulb (both cut into wedges) and 6 halved small shallots and cook until golden, 2 to 3 minutes. Stir in 1 teaspoon chopped thyme, 1/4 teaspoon allspice, 1 teaspoon kosher salt and a few grinds of pepper. Roast at 425˚ F, tossing once, until tender, 15 minutes. Add 1 more tablespoon butter and 2 tablespoons cider vinegar; toss until glazed, 1 minute. Top with fennel fronds.