Preheat the oven to 425°F. Bring a pot of lightly salted water to a boil.

Meanwhile, trim the bottoms of the fennel bulbs and cut off the green tops. Cut the bulbs vertically into slices ¾ inch thick. Add the fennel slices to the boiling water and cook until just tender enough to pierce with a fork but still firm, about 6 minutes. Drain thoroughly in a colander.

With a slotted spoon, transfer the fennel slices to a 2-quart casserole. Drizzle evenly with the melted butter and sprinkle with the minced garlic. Then drizzle with the vermouth and sprinkle evenly with half of the Parmesan. Bake uncovered until the fennel begins to brown, about 30 minutes.

Remove from the oven and serve topped with the remaining Parmesan.