Ingredients for the potato mixture
2 pounds Russet potatoes, peeled and sliced 1/8 inch thick
1 cup heavy cream
1 cup whole milk
2 cloves garlic, minced
1 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper
1/4 teaspoon ground nutmeg
1 1/2 cups Gruyere cheese, grated (or a blend of Gruyere and Parmesan)
4 tablespoons unsalted butter
Butter, for greasing baking dish
Thinly sliced Russet potatoes are standard for steakhouse-style and copycat Ruth’s Chris gratins because their starch content helps thicken the sauce and gives a silky texture once baked. Combining heavy cream and whole milk creates a rich but still pourable sauce that coats the potatoes without turning overly thick or chalky, similar to other high-end potato gratin recipes. Garlic, salt, black pepper, and nutmeg are classic flavorings in creamy gratins, adding warmth and complexity without overpowering the cheese.
Gruyere is often used in French-inspired gratins and many Parmesan-and-Gruyere potato dishes for its excellent melt and nutty, slightly sweet flavor. Adding some Parmesan to the Gruyere, if desired, boosts the salty, savory notes and helps form a nicely browned crust. Butter both enriches the sauce and is used to grease the baking dish to prevent sticking and encourage flavorful browning on the edges.
Step-by-step directions
Set the oven to 375°F (190°C). Generously butter a 9×13-inch baking dish, coating the bottom and sides to help prevent sticking and promote a golden edge on the potatoes, as recommended in many potato au gratin recipes.
Peel the Russet potatoes and slice them evenly to about 1/8 inch thick. A mandoline slicer gives consistent thickness, which helps the potatoes cook evenly and finish at the same time, a common tip in gratin instructions. If using a knife, aim for uniform slices and set the potatoes aside.
In a medium saucepan over medium heat, melt the 4 tablespoons of butter. Add the minced garlic and sauté for about 1 minute, just until fragrant, being careful not to brown it, since many steakhouse-style recipes note that browned garlic can add bitterness. Stir in the heavy cream and whole milk, whisking to combine. Add the kosher salt, black pepper, and ground nutmeg. Heat the mixture until it reaches a gentle simmer, but do not let it boil; heating the cream with the aromatics helps infuse flavor and can help prevent separation while baking. Once it is at a light simmer, remove the pan from the heat.
Arrange half of the potato slices in an even layer in the buttered baking dish, slightly overlapping them, similar to how other gratins layer thin slices for even cooking. Pour half of the warm cream mixture over this first layer, making sure the potatoes are evenly coated. Sprinkle half of the grated Gruyere (or Gruyere-Parmesan blend) over the top of the potatoes and sauce.
Repeat with the remaining potato slices, arranging them in a second even layer. Pour the rest of the cream mixture over the potatoes, then sprinkle with the remaining cheese to fully cover the top layer. Cover the dish tightly with aluminum foil and transfer it to the preheated oven.
Bake the potatoes covered for about 45 minutes, allowing the potatoes to cook through and the sauce to thicken gently. Remove the foil and continue baking for 15–20 minutes, or until the top is golden brown, the cheese is bubbling, and the potatoes are tender when pierced with a fork. Total baking time should be around 60–65 minutes, which aligns with many potato gratin and Ruth’s Chris–style recipes that call for roughly an hour in the oven.
Once done, remove the dish from the oven and let it rest for 5–10 minutes before serving. This rest time allows the sauce to settle and thicken slightly, making the gratin easier to scoop and helping it hold its shape on the plate, a common recommendation in creamy au gratin recipes. Garnish with chopped fresh parsley or thyme if desired and serve hot as a side dish alongside steak, roast chicken, or holiday mains.