Potato Gratin with Caramelized Onions and Fontina

Potato Gratin with Caramelized Onions and Fontina ingredients

• 2 large yellow onions, thinly sliced
• 2 tbsp unsalted butter
• 1 tbsp olive oil
• 2.5 lbs Russet or Yukon Gold potatoes, peeled and thinly sliced
• 2 cups Fontina cheese, shredded
• 2 cups heavy cream
• 0.5 cup whole milk
• 2 garlic clove, minced
• 1 tbsp fresh thyme leaves
• 0.25 tsp nutmeg, freshly grated
• 1 tsp kosher salt
• 0.5 tsp black pepper

How to make Potato Gratin with Caramelized Onions and Fontina

1. Begin by caramelizing the onions. In a large skillet, melt 2 tbsp unsalted butter with 1 tbsp olive oil over medium-low heat. Add the 2 thinly sliced large yellow onions and cook slowly for 30-40 minutes, stirring occasionally, until deeply golden brown and very soft. Set aside.
2. Preheat your oven to 375°F (190°C). Butter a 9x13-inch baking dish generously.
3. In a medium saucepan, combine 2 cups heavy cream, 0.5 cup whole milk, 2 minced garlic cloves, 1 tbsp fresh thyme leaves, 0.25 tsp freshly grated nutmeg, 1 tsp kosher salt, and 0.5 tsp black pepper. Heat over medium heat until it just begins to simmer, then remove from heat.
4. Thinly slice the 2.5 lbs peeled Russet or Yukon Gold potatoes, preferably using a mandoline for even thickness (about 1/8-inch). If slicing by hand, try to keep slices as uniform as possible.
5. Arrange one-third of the potato slices in a single, slightly overlapping layer on the bottom of the prepared baking dish. Top evenly with half of the caramelized onions, then sprinkle with one-third of the 2 cups shredded Fontina cheese.
6. Repeat with another layer of potatoes, the remaining caramelized onions, and another third of the Fontina cheese. Finish with the last layer of potatoes and the remaining Fontina.
7. Carefully pour the warm cream mixture evenly over the potatoes. Ensure the liquid is distributed well and peeks through the layers.
8. Cover the baking dish tightly with aluminum foil and bake for 45 minutes. This steams the potatoes and ensures they cook through.
9. Remove the foil and continue baking for another 20-30 minutes, or until the potatoes are tender when pierced with a knife, the top is golden brown, and the cream is bubbling. If the top is browning too quickly, you can loosely tent it with foil again.
10. Let the gratin rest for 10-15 minutes before serving. This allows the creamy sauce to set, preventing it from being too runny when scooped.

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