The Best Potato Mushroom Gratin

This is not your everyday scalloped potato dish. You layer the potatoes in along with salt and pepper Parm cheese and the whipping cream. You bake that off and then top with mushrooms more cheese and more whipping cream. You really do want to make this a day ahead and chill it which allows it to set up nicely. The potatoes go nicely with ham or beef and have a deep rich flavor.

Make the gratin one day ahead. Before serving, cut it into pieces and rewarm in the oven.

By allowing the dish to cool and then reheat it all of the moisture is kept in the potatoes and mushrooms, it is also easier to serve.

Potato mushroom gratin

The Best Potato Mushroom Gratin

Servings: 10


  • 5 Tablespoons / olive oil divided
  • 2 1/2 pounds / large potatoes peeled, cut lengthwise into 1/8-inch-thick slices (use a 4mm disc in your food processor)
  • 2 1/2 teaspoons / coarse kosher salt plus additional for mushrooms
  • 3/4 teaspoons / freshly ground black pepper plus additional for mushrooms
  • 1 cup / heavy whipping cream divided, may need more if it is dry
  • 1 cup / freshly grated Parmesan cheese (about 3 ounces), divided
  • 2 Tablespoons / chopped fresh thyme
  • 6 cloves / garlic thinly sliced
  • 12 ounces / fresh Cremini (baby bella) brown mushrooms sliced (Use 1 pound for doubled recipe)


  1. Preheat oven to 375°F. Brush 13x9x2-inch glass or oval ceramic baking dish (size matters so you get a uniform three layers) with 2 tablespoons oil.
  2. Arrange 1/3 of potatoes, slightly overlapping, in dish.
  3. Sprinkle with 1/2 teaspoon coarse salt and 1/8 teaspoon pepper.
  4. Pour 1/3 cup cream over;
  5. Sprinkle with 1/4 cup cheese.
  6. Repeat layering 1/3 of potatoes, 1/2 teaspoon salt, 1/4 teaspoon pepper, 1/3 cup cream, and 1/4 cup cheese 2 more times.
  7. Bake uncovered until potatoes are tender, adding cream by tablespoonfuls if dry, about 45 minutes. Remove from oven; maintain oven temperature.
  8. Sprinkle thyme and garlic slices over gratin. Toss mushrooms in medium bowl with 3 tablespoons oil; sprinkle with touch of coarse salt and pepper.
  9. Arrange mushroom slices atop gratin. Drizzle with 1/4 cup cream; sprinkle with 1/4 cup cheese.
  10. Continue to bake uncovered until mushrooms are tender and potato edges are golden brown, about 20 minutes longer.
  11. DO AHEAD: Can be made 1 day ahead. Cool 1 hour in dish; cover and chill. Before serving, cut gratin into 10 pieces. Transfer to rimmed baking sheet. Cover with foil and rewarm in 350°F oven, 10 to 15 minutes.