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+ servings

Potato and Caramelized Onion Gratin


  • 2 Tbsp unsalted butter
  • 1 Tbsp olive oil
  • 1 lb. yellow onions, thinly sliced (about 3 ½ cups)
  • sea salt + freshly ground black pepper
  • 2 lb. Yukon Gold potatoes (about 5 large)
  • 1 ½ tsp. chopped fresh thyme
  • 4 oz. grated Comté cheese (about 1 ½ cups)
  • 2 cups whole milk
  • pinch freshly grated nutmeg


  • Preheat the oven to 350° F

  • Caramelize the Onions
  • Heat 1 Tbsp of the butter and the olive oil in a 10-inch skillet over medium heat.
  • Add the onions and cook without stirring until beginning to brown (~ 5 to 7 minutes). Sprinkle with a strong pinch of sea salt and freshly ground black pepper
  • Reduce the heat to low and continue to cook, stirring and scraping the bottom of the pan frequently with a wooden spoon and spreading the onions evenly over the bottom of the skillet, until golden brown (~ 30 to 40 minutes)
  • Add 1 Tbsp water at a time if the onions begin to stick to the skillet.
  • Set aside to cool

  • Assemble and Bake the Gratin
  • Peel the potatoes. Using a mandoline or sharp knife, slice the potatoes into thin rounds (about 1/16 inch thick).
  • Spread about one-third of the potatoes in the bottom of a 3-quart baking dish. Sprinkle with sea salt, freshly ground black pepper and half of the thyme.
  • Scatter half of the caramelized onions evenly over the potatoes, and top with one-third of the cheese.
  • Make a second layer with half of the remaining potatoes.
  • Sprinkle with sea salt and freshly ground black pepper, and top with the remaining thyme and onions.
  • Top with one-third of the cheese.
  • Top with a third and final layer of potatoes.
  • In a 2-quart saucepan, bring the milk to a simmer. Stir in the nutmeg, and then pour the hot milk evenly over the potatoes.
  • Top with the remaining cheese.
  • Cut the remaining 1 Tbs. butter into small pieces and scatter on top.
  • Bake, until the potatoes are tender when pierced with a paring knife and the top, is golden brown (~ 1 hour to 1 ¼ hours)
  • Cover loosely with foil if the top begins to darken too quickly.
  • Let the gratin cool for 10 to 15 minutes before serving.