Caramelized Onion and Red Potato Cheesy Gratin Recipe

Servings: 6 to 8
Prep time: 20 minutes
Total time: 1 hour

10 tablespoons|140 grams unsalted butter
2 pounds|910 grams yellow onions, thinly sliced
1 teaspoon kosher salt, plus more to taste
2 garlic cloves, minced
2 ½ pounds|1200 grams large red potatoes, scrubbed clean and sliced about ⅛-inch thick
2 cups|500 ml half and half
3 sprigs fresh thyme
freshly ground black pepper, to taste
1 cup|80 grams grated gruyere cheese

1. Caramelize the onions: Melt 4 tablespoons of the butter in a large skillet over medium. Add the onions and a pinch of salt. Cook, stirring occasionally, until soft and translucent, 5 minutes. Continue cooking and stirring an additional 45 minutes, until the onions are dark golden. You may need to add a few tablespoons of water here and there to help loosen some of that good color from the bottom of the skillet and allow the onions to really soften. Once they’re dark golden brown, remove them from the heat and set aside.
2. Heat the oven to 375°F. Place the garlic on a cutting board with the teaspoon of salt and, using the side of the knife blade, smash the garlic over and over again until it forms a paste. Place the garlic in a large saucepan with the remaining 6 tablespoons butter, the potatoes, half and half, and 2 sprigs of thyme. Bring to a boil and cook until the potatoes are just soft and the mixture has thickened, 8 to 10 minutes. Stir the onions through and season with salt and pepper. Transfer to a 9-inch-by-13-inch baking dish and spread into an even layer. Top with the cheese and bake until the cheese is melted and golden and the mixture is bubbling, 25 to 30 minutes. Remove from the oven and cool slightly. Remove the leaves from the remaining sprig of thyme and sprinkle over the top to serve.

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