1 tablespoon unsalted butter, plus more for greasing dish
1 1/2 cups heavy cream
1 garlic clove, minced
2 pounds Yukon Gold potatoes, washed and thinly sliced
3/4 teaspoon thyme
1 pound mixed mushrooms, button, crimini and shiitake (your choice!)
1/4 cup grated Parmesan cheese
1 tablespoon olive oil
Sea salt and freshly ground pepper to taste
In a saucepan, combine the cream, garlic, thyme, and a pinch each of salt and pepper. Slowly bring to a boil over medium heat, stirring constantly. Remove from heat, gently stir in sliced potatoes and set aside.
Fry mushrooms in butter and add a pinch of salt.
Arrange one-third of the potato slices, slightly overlapping, on the bottom a prepared 8x8 baking dish. Sprinkle lightly with salt and pepper and 1 tablespoon of the cheese. Spread half of the mushrooms over the potatoes and sprinkle with 1 tablespoon of the cheese. Repeat these layers, using half of the remaining potatoes and all of the remaining mushrooms, and sprinkling with salt, pepper and 1 tablespoon of the cheese between the layers of vegetables.
Top with the remaining potatoes and sprinkle with salt and pepper. Using a large, flat spatula, gently press on the vegetables to compact them.
Pour the remaining cream mixture into the dish and sprinkle with the remaining cheese.
Cover with foil and bake at 375°F for 40 minutes until potatoes are tender.
Remove foil and bake an additional 15 minutes until brown and bubbly.