My French onion potato gratin recipe pairs the savory flavor of French onion soup with creamy potatoes and golden, cheesy edges. The trick is stacking the potato slices upright so more of each slice peeks above the cream. It's a cozy side dish worth making room for on your holiday table.
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My husband loved my balsamic caramelized onions so much I wanted to turn them into another side dish. For the onions, we build flavor with thyme, time (get it?), and a splash of balsamic. Yes, both kinds of thyme matter here. No onion soup mix required for fantastic French onions. Besides, it would overwhelm the dish and make it far too salty.
I use the same upright stacking technique in my Parmesan rutabaga gratin. You get tender slices underneath with exposed edges that brown on top, giving each serving a little texture.
This recipe is excellent served alongside sage-roasted turkey or my sous vide prime rib and a Dijon cream sauce.
📖Why My Recipe Works
- Standing the potatoes upright exposes more surface area than laying the slices flat. All about the texture and no flour makes it gluten free.
- Flavor built in the skillet. Caramelizing the onions and reducing the beef broth creates a concentrated base without a seasoning packet.
🧾Ingredient Notes
- Russet potatoes - Their starch helps thicken the cream as the gratin bakes. Choose similarly sized potatoes for more even slices and easier stacking. Yukon Gold potatoes are a nice option as well but they release less starch.
- Onions - Yellow or white onions are my first choice for their balance of sweetness and savory onion flavor. Sweet onions also work but give the finished gratin a sweeter flavor.
- Cheese - Gruyère brings the classic French onion soup flavor, while Parmesan adds a savory bite. Buy blocks and grate them fresh for smoother melting. You can substitute Swiss cheese for the Gruyère.
- Heavy cream - Creates a rich sauce around the potatoes. Stick with heavy cream for the intended consistency.
- Butter - Unsalted butter gives you control over the seasoning. And ensures the sodium in the broth doesn't overwhelm the dish.
- Fresh thyme - Adds a subtle herbal note that pairs especially well with caramelized onions. Substitute a small pinch of dried thyme if needed.
- Beef broth - Vegetable broth works as a substitute; for a fully vegetarian gratin, also choose cheeses made with vegetarian rennet.
- Balsamic vinegar - A small splash adds acidity and balances the onions' sweetness.
⏲️How to Make Potato and Onion Gratin
- Cut the onions into thin, even slices. Keeping them roughly the same thickness helps them cook at a similar rate.
- Don't rush caramelizing the onions. This is where the deep flavor will come from.
- Mixing the cheeses together ensures you get an even flavor.
- Toss the slices with the onions, cream, and about two-thirds of the cheese mixture. Separate any slices that stick together so the mixture can coat both sides.
- Pack the potatoes snugly enough to stay upright, distributing the onions between the slices as you go.
- Baking the potatoes covered will allow them to soften without drying them out.
- Uncover, add the reserved cheese, and broil until bubbly and browned in spots. Watch closely during this step; the topping can go from golden to scorched quickly.
👩🏻🍳Jen's Testing Notes
- If the onions start browning too quickly, lower the heat. You want gradual caramelization, not dark, burnt edges. You can always add a little water if needed.
- Cut the peeled potatoes into even, ⅛-inch slices. A mandoline makes this easier, in my opinion.
- Put the rack in the middle of the oven to prevent the bottom from burning
- Before adding the remaining cheese, slide a paring knife into the center of the gratin. It should pass through the potatoes easily. If you feel resistance, cover and continue baking until tender.
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📖 Recipe Card
French Onion Potato Gratin
Big flavor and the perfect texture. This potato onion gratin features upright potato slices baked with caramelized onions, cheese, and cream for a French onion potato gratin with tender centers and crispy edges. Homemade French onion flavor, no soup mix required. Perfect for holiday meals and Sunday dinners.
Servings: 8
Ingredients
Caramelized French Onions
- 2 Tablespoons unsalted butter
- 1 pound yellow onion thinly sliced
- ½ teaspoon kosher salt
- ¼ teaspoon black pepper
- 2 sprigs fresh thyme
- 2 cloves garlic minced
- ½ cup beef broth
- 1 teaspoon balsamic vinegar
Onion and Potato Gratin
- 3 pounds russet potatoes peeled and cut into ⅛ inch slices
- 1 ½ cups shredded gruyere cheese about 6 ounces
- ½ cup freshly grated parmesan cheese about 2 ounces
- 2 sprigs fresh thyme leaves removed
- ¾ cup heavy cream
Instructions
Caramelized French Onions
- Melt the butter in a 12-inch heavy-bottomed skillet over medium heat. Add the onions, thyme, salt, and pepper. Cook, stirring frequently until the onions are very soft, and deep golden-brown, 25 to 30 minutes. If the onions begin to burn turn down the heat and stir more often.2 Tablespoons unsalted butter, 1 pound yellow onion, ½ teaspoon kosher salt, ¼ teaspoon black pepper, 2 sprigs fresh thyme
- Add the garlic and cook for 1 minute. Add the beef broth, scrape up any brown bits. Bring the broth to a boil and simmer until it is reduced by half. Remove from heat, remove the thyme sprigs, and stir in the balsamic.2 cloves garlic, ½ cup beef broth, 1 teaspoon balsamic vinegar
Onion and Potato Gratin
- Preheat oven to 400 F degrees. Grease a 12 inch casserole dish or cast iron pan with butter.
- Mix together the two cheeses and fresh thyme in a small bowl.1 ½ cups shredded gruyere cheese, ½ cup freshly grated parmesan cheese
- In a large bowl combine the potato slices, caramelized onions, cream, and roughly ⅔ of the cheese mixture. Do your best to break up the potato slices so that each slice is covered with the cream mixture.3 pounds russet potatoes
- Layer the potato slices into sideways stacks in the baking dish. They should be tight enough that the slices stay upright. If not, slice up an additional potato and add it. Spoon over any cheese or onions remaining in the bowl then pour over the cream from the bottom of the bowl.¾ cup heavy cream
- Cover with foil and bake for 60 minutes. Uncover and top with the remaining cheese. Broil the gratin until the cheese is bubbly and browned in spots, about 5 to 6 minutes. Remove from oven. Let rest for 15 minutes before serving. Garnish with additional fresh thyme if desired.2 sprigs fresh thyme
Notes
- The onions can be made two days in advance, but bring to room temperature for easier assembly.
- Store leftovers in an airtight container in the refrigerator for up to 4 days. Reheat covered at 350°F until heated through, then uncover for the last few minutes to help crisp the top.
Equipment
- 12-inch heavy-bottomed skillet
- 12-inch casserole dish or cast iron pan
Nutrition
Serving: 1g | Calories: 405kcal | Carbs: 38g | Protein: 15g | Fat: 22g | Fiber: 3g | Sugar: 4g
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Common Recipe Questions
Can I make potato gratin in advance?
You can make the onions 2 days ahead. If you want to make the potatoes ahead, bake until almost done, cool completely, then cover tightly and refrigerate for up to 48 hours. Let sit at room temperature for 30 minutes before reheating at 350°F until heated through. Then add the cheese on top and broil
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