Name: Caramelized Onion Potatoes au Gratin Recipe
Prep time: 25 min
Cook time: 55 min
Total time: 1 h 20 min
Cuisine: French
Ingredients: 4 tablespoons unsalted butter, divided; 2 sweet yellow onions, thinly sliced; 1 teaspoon sugar; 4 lbs large russet potatoes (about 4-7), peeled and sliced about 1/8″ (3mm) thick on a mandoline; 2 1/2 cups heavy cream; 1 1/2 cups half & half; 3 garlic cloves, grated; 2-3 sprigs fresh thyme; 2 bay leaves; Pinch of nutmeg; Kosher salt, to taste; Freshly ground black pepper, to taste; 6 oz Gruyere cheese, shredded

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Introduction

This Caramelized Onion Potatoes au Gratin is a rich and comforting dish perfect for any occasion. Creamy, cheesy, and infused with the sweet depth of caramelized onions, it’s an elevated twist on a classic favorite. Ideal as a side or a hearty main, it will become a family favorite.

A creamy baked dish is shown in a round green bowl with a handle, filled with layers of melted cheese on top. The top layer is golden brown with bubbly, slightly crispy cheese patches that have darker toasted spots, mixed with small green thyme leaves scattered over. Below the cheese, a thick, creamy sauce with a smooth texture is visible, speckled with ground black pepper. The bowl sits on a white marbled surface, next to a white textured plate with two gold forks. Photo taken with an iphone --ar 4:5 --v 7

Ingredients

4 tablespoons unsalted butter, divided
2 sweet yellow onions, thinly sliced
1 teaspoon sugar
4 lbs (about 4-7) large russet potatoes, peeled and sliced about 1/8″ thick (3mm) on a mandoline
2 1/2 cups heavy cream
1 1/2 cups half & half
3 garlic cloves, grated
2-3 sprigs of fresh thyme
2 bay leaves
Pinch of nutmeg
6 oz gruyere cheese, shredded
Kosher salt
Freshly ground pepper

Instructions

Step 1: In a medium skillet, melt 2 tablespoons of butter over medium-low heat. Add the sliced onions and toss to coat. Cover the pan for 5 minutes to help the onions wilt. Season with salt and pepper, cook stirring occasionally until onions turn golden brown. Sprinkle with sugar and continue cooking until onions are a deep amber color. Set aside to cool.
Step 2: In a 4-quart pot or Dutch oven, combine the heavy cream, half & half, grated garlic, thyme sprigs, bay leaves, and nutmeg. Season with salt and pepper. Add the sliced potatoes and bring to a gentle simmer over low heat. Simmer for 15 minutes, or until the potatoes are just beginning to become tender. Taste and adjust seasoning as needed. Remove from heat and let rest for 10 minutes.
Step 3: Preheat the oven to 375°F (190°C). Butter a 3-quart baking dish with the remaining 2 tablespoons of butter and set aside. Remove and discard the thyme sprigs and bay leaves from the potatoes.
Step 4: Using a slotted spoon, transfer half of the potatoes to the baking dish. Layer half of the caramelized onions and half of the shredded cheese on top. Add the remaining potatoes to cover. Pour the remaining creamy sauce over the potatoes, then top with the remaining onions and cheese. Bake uncovered for 35-40 minutes, until the cheese is bubbly and golden and the potatoes are tender.
Step 5: Allow the gratin to rest for 15 minutes before serving. Garnish with fresh thyme if desired.

Tips & Variations

For extra flavor, use a mix of gruyere and sharp cheddar cheese.
Try adding a pinch of smoked paprika for a subtle smoky note.
If you prefer a thinner sauce, reduce the simmering time of the potatoes slightly.
Use Yukon Gold potatoes for a creamier texture instead of russets.

Storage

Store any leftovers in an airtight container in the refrigerator for up to 3 days. Reheat gently in the oven at 350°F (175°C) until warmed through to maintain the crispy cheese topping. This dish does not freeze well due to the cream sauce.

How to Serve

A close-up of a creamy potato gratin in a green dish with a handle, showing multiple thin layers of tender potato slices covered in melted golden-brown cheese on top with some small green herb sprigs scattered for garnish. A silver spoon scoops up a portion, revealing tightly stacked off-white potato layers with a smooth creamy sauce in between, and a slightly browned crust on the surface. The dish sits on a white marbled texture with two glass salt and pepper shakers nearby, and part of a white textured plate visible on the side. photo taken with an iphone --ar 4:5 --v 7

Serve this delicious recipe with your favorite sides.

FAQs

Can I prepare this dish ahead of time?

Yes, you can assemble the gratin a few hours ahead and keep it covered in the refrigerator. Bake just before serving for best results.

What can I substitute for gruyere cheese?

Swiss cheese, fontina, or a mild white cheddar work well as substitutes and will provide a similar creamy melt and flavor.