Ruth’s Chris–Style Caramelized Onion & Gruyère Potato Gratin

Instructions:

1. Preheat the oven to 375°F (190°C) and generously butter a deep baking dish.
2. In a large skillet over medium-low heat, melt the butter with the olive oil.
3. Add the sliced onions and cook slowly, stirring occasionally, for 20 to 25 minutes until deeply golden and caramelized. Remove from heat and set aside.
4. In a saucepan, combine the heavy cream, milk, garlic, salt, pepper, and nutmeg. Warm gently over low heat, being careful not to boil.
5. Arrange half of the sliced potatoes evenly in the prepared baking dish.
6. Spread half of the caramelized onions over the potatoes.
7. Sprinkle with half of the Gruyère cheese and a portion of the Parmesan.
8. Repeat the layers with the remaining potatoes, onions, and cheeses.
9. Pour the warm cream mixture evenly over the layered potatoes, gently pressing them down so they are mostly submerged.
10. Cover the dish tightly with foil and bake for 45 minutes.
11. Remove the foil and continue baking for 20 to 25 minutes, until the top is golden, bubbly, and the potatoes are fork-tender.
12. Let the gratin rest for 10 minutes before serving. Garnish with fresh thyme or parsley if desired.

Variations

• Add thinly sliced shallots along with the onions for extra depth of flavor.
• Substitute half of the Gruyère with Fontina or Emmental for a slightly different cheese profile.
• Layer in cooked bacon or pancetta for a smoky, savory twist.
• Use half-and-half instead of heavy cream for a lighter version.

Tips

• Slice the potatoes evenly to ensure uniform cooking.
• Keep the heat low when caramelizing onions to avoid burning and develop maximum sweetness.
• Letting the gratin rest before serving helps the layers set and makes slicing easier.
• For an authentic steakhouse finish, broil for 2 to 3 minutes at the end until the top is deeply golden and lightly crisp.