Chef John's Truffled Potato Gratin

Ingredients

• 1.33 tablespoons unsalted butter
• 1 tablespoon olive oil
• 5 cups sliced mushrooms
• 2 teaspoons unsalted butter , softened
• 1 clove garlic , Optional
• 5 russets potatoes , peeled and very thinly sliced
• 1 teaspoon minced fresh thyme leaves
• salt and freshly ground black pepper to taste
• 6 ounces sottocenere , Italian semi-soft truffle cheese
• 2 cups heavy whipping cream
• 1 cup chicken stock

Instructions

1. 1

   Melt 1 1/3 tablespoons butter with olive oil in a large saucepan over medium-high heat; add mushrooms. Cook, stirring often, until edges browned, 15 to 20 minutes.

2. 2

   Preheat the oven to 350 degrees F (175 degrees C).

3. 3

   Combine 2 teaspoons softened butter and garlic in a small bowl. Grease a 9x13-inch baking dish with garlic butter.

4. 4

   Layer 1/3 potatoes into the prepared baking dish; season with 1/2 thyme, salt, black pepper, and 1/2 cooked mushrooms. Reserve 3 tablespoons sottocenere cheese for top and set aside; layer 1/2 remaining cheese over mushrooms. Layer 1/3 potatoes over cheese; season with remaining 1/2 thyme, salt, black pepper, remaining 1/2 cheese, remaining 1/2 mushrooms, and remaining 1/3 potatoes. Season with salt and black pepper. Pour cream and chicken stock over top; season with salt and black pepper. Top with reserved 3 tablespoons cheese. Cover dish loosely with aluminum foil; tent foil a little so it doesn't touch potatoes.

5. 5

   Bake in the preheated oven until potatoes are bubbly, about 45 minutes. Remove foil and cook until top is browned, about 15 minutes more. Cool slightly before serving.