Chef John's Truffle Potato Gratin

Heat the saucepan over medium-high heat, then combine 1 and a quarter tablespoons of melted butter with olive oil; cook the mushrooms in this mixture, stirring frequently, until they are nicely browned on their edges, taking around 15 to 20 minutes.

Preheat the oven to a temperature of three hundred and fifty degrees Fahrenheit. In another bowl, mix two teaspoons of softened butter with garlic; use this mixture to grease a 9x13-inch baking dish.

Place one third of the potatoes at the bottom of the prepared baking dish in a layer; add some salt, black pepper, one half of the thyme leaves, and one half of the cooked mushrooms. Sprinkle almost half of the sottocenere cheese over the potatoes, reserving about three tablespoons for the top. Add another layer of one third of the potatoes over the cheese, season with salt and black pepper, remaining half of the thyme leaves, remaining half of the cheese, remaining mushrooms, and lastly, a layer of potatoes. Season the potatoes with some extra salt and black pepper. Pour chicken stock and cream over the top, sprinkle with more salt and black pepper and the reserved three tablespoons of sottocenere cheese. Cover the dish loosely with aluminum foil, and gently shape it to prevent the potatoes from touching the foil.