Chef John's Root Vegetable Gratin

Step 1
Preheat the oven to 375 degrees F (190 degrees C).

Step 2
Bring a large pot of generously salted water to a boil. Add the vegetables, and cook uncovered for 3 minutes. Drain in a colander, then immediately immerse in ice water for several minutes until cold to stop the cooking process. Once the vegetables are cold, drain well, and set aside.

Step 3
Cook garlic and butter in a large skillet over medium heat until garlic starts sizzling, about 3 minutes.

Step 4
Stir in chicken broth, heavy cream, thyme, nutmeg, and cayenne pepper; cook until mixture begins to simmer, about 5 minutes.

Step 5
Coat a 9×13-inch baking dish with olive oil and spread vegetables evenly over the oil.

Step 6
Pour broth and cream mixture over vegetables and top with half of the grated Parmigiano-Reggiano cheese.

Step 7
Cover baking dish loosely with aluminum foil, place on a baking sheet, and bake in the preheated oven for 40 minutes.

Step 8
Remove baking dish from the oven and top with remaining Parmigiano-Reggiano. Bake uncovered until vegetables are browned, bubbling, and tender, about an additional 30 minutes.

Step 9
Remove from the oven and let rest for 20 minutes.