Creamy Potato and Mushroom Gratin with Garlic & Thyme
This luxurious Potato and Mushroom Gratin is the ultimate comfort food side dish. Featuring tender layers of Yukon Gold potatoes simmered in heavy cream and Parmesan, it’s topped with earthy, garlic-scented crimini mushrooms and fresh thyme. Whether you're planning a sophisticated Sunday roast or looking for the perfect make-ahead holiday side dish, this rustic yet elegant gratin delivers deep umami flavor and a velvety texture in every bite.
Equipment
- 13x9x2 inch glass or ceramic baking dish
- Mandoline slicer optional but recommended
- Medium mixing bowl
- Pastry brush
Ingredients
- 5 tbsp olive oil divided
- 6 garlic cloves thinly sliced
- 3/4 tsp freshly ground black pepper plus extra for mushrooms
- 2 1/2 lbs medium Yukon Gold potatoes peeled and sliced 1/8 inch thick
- 1 1/2 tsp coarse kosher salt plus extra for mushrooms
- 1 1/4 cups or more heavy whipping cream, divided
- 12 oz fresh crimini baby bella mushrooms, sliced
- 1 cup freshly grated Parmesan cheese divided
- 2 tbsp chopped fresh thyme
Instructions
- Prep the Base: Preheat oven to 375°F. Brush your baking dish with 2 tbsp of olive oil.
- Layer the Potatoes: Arrange 1/3 of the potatoes in the dish, slightly overlapping. Sprinkle with 1/2 tsp salt and 1/4 tsp pepper. Pour 1/3 cup cream over them and sprinkle with 1/4 cup Parmesan.
- Repeat Layers: Repeat this process two more times (3 layers total).
- First Bake: Bake uncovered for 45 minutes or until potatoes are tender. If they look dry, add a splash more cream.
- Prep Topping: In a bowl, toss sliced mushrooms with 3 tbsp olive oil, salt, and pepper.
- Final Bake: Sprinkle sliced garlic and thyme over the gratin. Arrange mushrooms around the edges. Drizzle with the remaining 1/4 cup cream and 1/4 cup Parmesan.
- Finish: Bake for another 20 minutes until mushrooms are tender and edges are golden brown.
- Rest: Let rest for 10 minutes before slicing to allow the cream to set.