Description

This Potato & Mushroom Gratin is a creamy, cheesy baked casserole featuring thinly sliced russet potatoes layered with sautéed portabello mushrooms and a rich herb-infused cream sauce. Topped with a blend of Swiss, Gruyere, and Parmesan cheeses, this gratin is golden and bubbly after baking, perfect as a comforting side dish or elegant vegetarian main course.

Ingredients

Scale

Vegetables

5 medium russet potatoes, sliced thinly (⅛ inch thick)
8 ounces portabello mushrooms, sliced

Dairy & Cheese

1 ½ cups heavy cream
½ cup shredded Swiss cheese
½ cup shredded Gruyere cheese
2 tablespoons grated Parmesan cheese

Seasonings & Oils

1 tablespoon olive oil
1 teaspoon thyme
1 teaspoon minced fresh garlic
Salt and pepper, to taste

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Instructions

Preheat the oven: Set your oven temperature to 400°F (204°C). Lightly spray a 2-quart oval baking dish with cooking spray to prevent sticking and set it aside to prepare for layering.
Sauté the mushrooms: Heat the olive oil in a small skillet over medium heat. Add the sliced portabello mushrooms and cook for 5-6 minutes, allowing the mushrooms to release their moisture and soften. Once done, remove the skillet from heat and set mushrooms aside.
Prepare the cream sauce: In a small saucepan, combine the heavy cream, minced fresh garlic, and thyme. Warm the mixture over medium heat until it is heated through but not boiling. Season the cream sauce with salt and pepper to your preference.
Arrange the potatoes: Peel the potatoes and slice them into ⅛ inch thick slices if not already done. Place the sliced potatoes evenly in the prepared baking dish as the base layer.
Assemble the gratin: Pour the warm cream sauce evenly over the potatoes in the baking dish. Sprinkle the shredded Swiss and Gruyere cheeses evenly on top, followed by the sautéed mushrooms. Finish by sprinkling the grated Parmesan cheese over the entire dish.
Bake the gratin: Place the baking dish in the preheated oven and bake for 45 minutes or until the top is golden brown and bubbly. After baking, let the gratin rest for 10 minutes before serving to allow it to set.

Notes

For best results, slice the potatoes as uniformly as possible to ensure even cooking.
If preferred, substitute Gruyere with another melting cheese like mozzarella or fontina.
You can prepare the gratin a few hours ahead; refrigerate uncovered before baking and increase baking time slightly.
Allowing the gratin to sit after baking improves texture and makes serving easier.
Use fresh thyme for optimal flavor, but dried thyme can be substituted at one-third the amount.