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
Calories: 405kcal
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.
- 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.
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.
- 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.
- 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.
- 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.
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.
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