This gorgeous casserole dish ofPotatoes Au Gratin with Caramelized Onions is a little more sophisticated, and tastier, than it's scalloped potato cousin but just as easy to prepare and equally family friendly. Soul-satisfying, comforting, and nostalgic, this is hands down the best gratin dish you'll ever taste.
Prep Time30 minutesmins
Cook Time2 hourshrs15 minutesmins
Total Time2 hourshrs45 minutesmins
Servings: 8
Ingredients
1tablespoonunsalted butter
2tablespoonsolive oil
1medium Spanish onion (or a large yellow onion)halved and thinly sliced crosswise
2 1/4cupsheavy cream
2teaspoons Kosher salt
freshly ground black pepper
3poundsrusset potatoes(4-5 large potatoes)
2cupsgrated Gruyère cheese
chopped fresh thymeoptional, for garnish
Instructions
In a medium/large skillet, heat butter and oil over medium-low heat. Cook onion slices, stirring often, until light golden-brown, about 25 minutes.
When onions are almost done caramelizing, preheat oven to 375ºF.
Heat the cream with 2 teaspoons salt and 1/2 teaspoon freshly ground pepper in a medium saucepan over medium heat. Simmer for 3 to 4 minutes then remove from heat.
Peel and slice potatoes into 1/8-inch thick rounds (a mandoline makes this job easy).
Layer half of the potatoes slices in the prepared casserole dish making sure to separate any slices that are sticking together. Pour half of the warm cream over the potatoes; top with all of the caramelized onion and a little more than half of the cheese. Layer the remaining potato slices on top and drizzle all the remaining cream evenly over the potatoes. Push down gently on the potatoes with your hands to ensure they are all submerged in the cream. Sprinkle with remaining cheese.
Cover tightly with foil and bake for 1 hour. Remove foil and bake until potatoes are tender and golden brown, about 30 minutes longer.
Remove from oven and let rest for a few minutes. Garnish with fresh thyme, if using, and serve warm.
Notes
Recipe adapted from The Barefoot Contessa CookbookMake AheadPotatoes au gratin can easily be made ahead. The trick is to be sure the potatoes slices are completely immersed in sauce, and covered tightly, so they don't turn brown.Simply assemble the entire dish, cover tightly with plastic wrap, and refrigerate for up to 24 hours. Bake as instructed adding about 10 minutes to the cooking time.Alternatively, bake the dish a day or two ahead, then reheat in a 350º, covered in foil, until warmed through. Reheating the potatoes au gratin makes them a little less creamy but they will still be delicious.