This Roasted Garlic Potatoes au Gratin is the kind of dish that changes how your family thinks about potatoes. I first developed this version during a chilly November when I wanted something richer than mashed potatoes but still entirely comforting. The head of garlic softens and caramelizes in the oven, turning into a mellow, sweet paste that infuses the cream with gentle roasted garlic flavor. The texture comes from thin, even slices of starchy potatoes layered upright so every bite has a tender interior and slightly crisp top edge.

I often make this for holiday dinners and midweek family suppers alike. What makes it special is the balance of technique and forgiveness: precise when you want it to be—use a mandoline for consistently thin slices—but forgiving enough that it still tastes great if a slice is a little thick. The combination of heavy cream, whole milk, butter, nutmeg and plenty of Gruyère brings nutty, savory richness while thyme adds a light, herbaceous lift. Serve it with roasted meats or a crisp salad and it becomes the star of the table.

Ingredients

• Potatoes: 8 to 9 medium starchy potatoes (about 2.6 pounds), ideally Russets for their high starch content and tender, creamy texture when baked. Look for medium-sized tubers so slices stack evenly; if you prefer waxy potatoes the texture will be firmer and less fluffy.
• Garlic: 1 head roasted whole to develop a mellow, caramelized paste that disperses through the sauce. Roasting concentrates sweetness and removes sharp bite.
• Heavy cream: 1 cup for luscious richness; do not substitute skim or the sauce will lack body.
• Whole milk: 1/4 cup to slightly loosen the cream so it penetrates between the slices without becoming soupy.
• Unsalted butter: 1 tablespoon to finish the sauce and grease the dish; use European-style butter for extra flavor.
• Fresh thyme leaves: 1 teaspoon for a light herbal note; strip leaves from the stems for best texture.
• Nutmeg: 1/4 teaspoon freshly grated for warmth that complements dairy and cheese.
• Cheese: 2 cups shredded Gruyère for nuttiness and excellent melting; mozzarella can be used for a milder, stringier finish.
• Salt and pepper: To taste; kosher salt and freshly ground black pepper yield the best control.

Instructions

Preheat and roast the garlic: Preheat the oven to 375 degrees Fahrenheit. Trim the top quarter off the head of garlic to expose the cloves, drizzle with a little olive oil, sprinkle with salt, wrap tightly in foil and roast on a small baking sheet for about 30 minutes until cloves are soft and lightly browned. Roasting time varies by garlic size; a fully soft center indicates readiness. Prepare the dish and slice potatoes: Grease a 9 by 13-inch baking dish with 1 tablespoon of butter. Using a mandoline set to about 1/8 inch, slice peeled potatoes into even rounds. Consistency is key: uniform slices ensure even cooking. Arrange slices upright in the dish in overlapping rows to create air pockets that help the sauce circulate. Make the cream mixture: In a medium saucepan over low heat combine 1 cup heavy cream, 1/4 cup whole milk, 1 tablespoon butter, 1 teaspoon fresh thyme leaves, 1/4 teaspoon grated nutmeg, salt and black pepper to taste, and half of the shredded cheese (about 1 cup). Heat gently until the butter melts and the cheese begins to incorporate; do not boil. Squeeze the roasted garlic cloves from their skins into a paste and whisk into the warm cream until smooth. Assemble and bake covered: Pour the warm cream mixture evenly over the arranged potato slices, allowing it to settle between layers. Cover the dish tightly with foil and bake at 375 F for about 40 minutes. This gentle covered phase softens the potatoes through without browning. Finish uncovered and brown: Remove the foil, sprinkle the remaining 1 cup of shredded cheese over the top, and bake uncovered for an additional 30 minutes until the sauce is bubbling and the top is golden brown. If the top browns too quickly, tent with foil to prevent burning while the interior finishes cooking. Rest and serve: Allow the gratin to rest for 10 to 15 minutes so the sauce thickens and the slices hold together. Garnish with chopped fresh chives or extra thyme before serving.

Storage Tips

Cool the gratin to room temperature before storing to prevent condensation. If you have leftovers, cover tightly with foil or transfer to an airtight container and refrigerate for up to 4 days. To reheat, warm at 325 degrees Fahrenheit covered for 20 to 30 minutes, then uncover for 10 minutes to restore the browned top. For freezing, wrap the dish well in plastic and foil or transfer to a freezer-safe container and freeze for up to 3 months; thaw overnight and bake at 350 F until heated through, about 45 to 60 minutes depending on size.

Ingredient Substitutions

If you do not have Gruyère, Emmental or a good-quality Swiss cheese are both excellent alternatives that melt smoothly and add a nutty character. For a milder, budget-friendly option use whole-milk mozzarella combined with a bit of sharp cheddar for flavor. Replace heavy cream with a mixture of half-and-half and a little cream cheese in a pinch; this affects richness and mouthfeel but still yields a creamy dish. To make it lighter, swap half the cream for low-fat milk but expect a less luxurious texture.

Serving Suggestions

This pairs beautifully with roasted or braised meats such as roast chicken, beef tenderloin, or glazed ham. Add a bright green salad with a lemon vinaigrette or roasted Brussels sprouts to contrast the richness. For holiday tables, serve in its baking dish garnished with finely chopped chives and a few fresh thyme sprigs. For a special presentation, portion the gratin into individual ramekins and broil briefly for a crisp top.

Cultural Background

Potatoes au gratin has its roots in French provincial cooking where simple ingredients are elevated through technique—layers of potatoes baked in cream until golden. The term au gratin refers to the crusty browned top, traditionally achieved with breadcrumbs or cheese. This Americanized version emphasizes roasted garlic and Gruyère, bridging French technique with the hearty comfort food sensibilities cherished in many family kitchens.

Seasonal Adaptations

In winter, add roasted root vegetables like parsnips or chopped roasted leeks for additional heartiness. In spring or summer, lighten the dish by adding a handful of fresh spinach between layers and using 3/4 cup cream plus 1/2 cup whole milk. For a festive holiday twist fold in a tablespoon of Dijon mustard into the cream for tang and depth. Fresh herbs change the profile—swap thyme for rosemary in small amounts for an earthier note.

Meal Prep Tips

Assemble the gratin a day ahead and keep covered in the refrigerator; bring to room temperature while the oven preheats and extend the baking time by 10 to 20 minutes. If you plan to freeze unbaked, flash-freeze individual portions on a tray and then transfer to freezer bags for quicker reheating. Use shallow, oven-safe containers for meal prep portions so they reheat evenly. Label with date and reheat with a little extra cream if the mixture looks dry.

The joy of this dish is its combination of technique and heart: simple ingredients transformed into something memorable. Make it your own by adjusting cheese or herbs, and enjoy the warm, cheesy comfort it brings to the table.