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

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Prep Time: 30 minutes | Cook Time: 1 hour 30 minutes | Total Time: 2 hours
Skill Level: Intermediate | Serves: 8 | Calories per Serving: ~420

A Note on This Recipe

Inspired by the iconic, decadent sides served at Ruth’s Chris Steak House, this potato gratin is the ultimate indulgence. Thinly sliced potatoes are layered with sweet, slow-cooked caramelized onions and nutty Gruyère cheese, then bathed in a rich cream mixture. The result is a luxurious, bubbling casserole with a golden-brown crust and a tender, savory interior. It’s the perfect centerpiece for a holiday table or a special Sunday dinner.

Ingredients

For the Caramelized Onions:

  • 2 tablespoons unsalted butter

  • 2 large yellow onions, thinly sliced

  • 1 teaspoon kosher salt

  • ½ teaspoon granulated sugar (to aid caramelization)

  • 1 tablespoon dry sherry or white wine (optional)

For the Gratin:

  • 3 lbs Yukon Gold potatoes, peeled

  • 2 cups heavy cream

  • 1 cup whole milk

  • 2 cloves garlic, minced

  • 1 teaspoon fresh thyme leaves, plus more for garnish

  • 1 ½ teaspoons kosher salt

  • ½ teaspoon freshly ground black pepper

  • ¼ teaspoon freshly grated nutmeg

  • 2 ½ cups freshly grated Gruyère cheese, divided

  • ½ cup freshly grated Parmesan cheese

Equipment:

  • Mandoline slicer (recommended for even slices)

  • 9×13 inch baking dish or 3-quart gratin dish

  • Large skillet

Instructions

Step 1: Caramelize the Onions (20-25 minutes)

This step cannot be rushed. True, deep flavor comes from patience.

  1. In a large skillet over medium-low heat, melt the butter.

  2. Add the sliced onions, salt, and sugar. Stir to coat.

  3. Cook, stirring occasionally, for 20-25 minutes. The onions will first soften, then release their juices, and finally turn a deep golden brown. Reduce heat if they begin to burn.

  4. If using, add the sherry or wine in the last 2 minutes to deglaze the pan, scraping up any browned bits. Set aside.

Step 2: Prepare the Cream Mixture & Potatoes (15 minutes)

  1. Preheat your oven to 375°F (190°C).

  2. In a medium saucepan, combine the heavy cream, milk, minced garlic, thyme, salt, pepper, and nutmeg. Warm over medium heat until just beginning to simmer. Remove from heat.

  3. Using a mandoline or a very sharp knife, slice the peeled potatoes into 1/8-inch thick rounds. Important: Do not rinse the slices; the surface starch is crucial for thickening the cream.

Step 3: Assemble the Gratin (10 minutes)

  1. Lightly grease your baking dish.

  2. Spread about one-third of the potato slices in a slightly overlapping layer on the bottom of the dish.

  3. Sprinkle with one-third of the caramelized onions and ¾ cup of the grated Gruyère.

  4. Pour over about one-third of the warm cream mixture.

  5. Repeat these layers two more times, ending with a final layer of potatoes and the remaining cream mixture.

  6. For the top, combine the remaining ¼ cup Gruyère with the ½ cup Parmesan. Sprinkle evenly over the entire surface.

Step 4: Bake to Perfection (60-75 minutes)

  1. Cover the dish tightly with aluminum foil and place on a baking sheet (to catch any drips).

  2. Bake, covered, for 45 minutes. This steams the potatoes until tender.

  3. Remove the foil and continue baking, uncovered, for another 15-30 minutes, or until the top is deeply golden brown, the cream is bubbling vigorously around the edges, and a knife slides easily through the potato layers.

  4. The Key Rest: Once out of the oven, let the gratin rest for at least 20 minutes. This allows the cream sauce to thicken properly and sets the layers, making it much easier to serve clean slices.

Serving & Pairing Suggestions

Garnish with a sprinkle of fresh thyme. This gratin is the perfect rich companion to simply cooked proteins that can stand up to its bold flavor:

  • Classic: A perfectly seared ribeye or filet mignon.

  • Holiday: Roasted prime rib or herb-crusted leg of lamb.

  • Lighter Option: A peppery arugula salad with a lemon vinaigrette to cut through the richness.

Nutrition Information (Per Serving)

  • Calories: 420

  • Total Fat: 32g

  • Saturated Fat: 19g

  • Cholesterol: 105mg

  • Sodium: 620mg

  • Total Carbohydrates: 25g

  • Dietary Fiber: 2g

  • Sugars: 5g

  • Protein: 14g

Nutritional information is an estimate based on the ingredients listed and may vary based on specific brands and portion sizes.

Chef’s Notes & Make-Ahead Tips

  • Make-Ahead Magic: Assemble the entire gratin (up to adding the final cheese topping) 1 day in advance. Cover and refrigerate. Let sit at room temperature for 30 minutes, add the cheese topping, and bake as directed, adding 5-10 minutes to the covered baking time.

  • Leftovers: Store covered in the refrigerator for up to 4 days. Reheat individual portions in a skillet for the best texture, or cover the whole dish with foil and warm in a 325°F oven until heated through.

  • No Mandoline? Use the slicing side of a box grater or take your time with a knife. Consistency is key for even cooking.

Enjoy the taste of steakhouse luxury in the comfort of your own home.

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