Step 1Heat the oven to 400 degrees.
Step 2Cut the pumpkin in half and remove the seeds, then peel it with a potato peeler or paring knife. Lay the cut side down and cut it into half-inch wide slices. Lay the slices flat and cut them into 1-inch pieces.
Step 3Place the pumpkin in a very large mixing bowl and add the thyme, garlic, Aleppo pepper, sea salt and pepper. Toss to mix.
Step 4Add the panko and one-half cup of the Gruyere and toss again, mixing well. Pour the cream over and toss until all the ingredients are evenly coated.
Step 5Butter a large gratin dish or a 13-by-9-inch baking dish. Spread the pumpkin mixture evenly in pan. Sprinkle the remaining Gruyere over the top.
Step 6Bake until the pumpkin is caramelized and tender, but not mushy, and the cheese is browned, 35 to 40 minutes. Serve hot or warm, garnished with sprig of thyme.