Ingredients:
- lbs (1.35 kg) Russet or Yukon Gold Potatoes, peeled
- cups Heavy Cream
- cup Whole Milk
- cloves Garlic, finely minced
- sprigs Fresh Rosemary, leaves stripped and roughly chopped
- teaspoons White Truffle Oil
- /4 teaspoon Freshly Grated Nutmeg
- teaspoons Kosher or Sea Salt
- /2 teaspoon Freshly Ground Black Pepper
- cup (100 g) Freshly Grated Gruyère or Comté Cheese
- tablespoon Unsalted Butter, for greasing
- /2 cup (60 g) Raw Hazelnuts, roughly chopped
- teaspoon Fresh Rosemary, finely chopped leaves (for topping)
- /2 cup (120 g) Crème Fraîche, for drizzling
Instructions:
- Preheat oven to 375°F (190°C). Generously butter the 9x13 inch baking dish. Peel and slice potatoes very thinly (about 1/8 inch or 3mm thick); use a mandoline if possible for uniformity.
- In a saucepan, combine cream, milk, minced garlic, chopped rosemary, nutmeg, salt, and pepper. Heat gently until simmering around the edges. Remove from heat, stir in the truffle oil, and let steep for 10 minutes. Strain the cream mixture to remove most of the garlic and rosemary pieces.
- Arrange one-third of the sliced potatoes snugly in the bottom of the prepared dish, overlapping slightly. Sprinkle with one-third of the grated cheese. Repeat this layering process twice more.
- Slowly and evenly pour the warm, infused cream mixture over the layered potatoes, ensuring the liquid seeps down. Press down gently with a spatula.
- Cover the dish tightly with foil. Bake for 50 minutes.
- Remove the foil. Continue baking for another 25–35 minutes, or until the top is golden brown and a knife inserts easily through the centre.
- While the gratin finishes baking, toast the chopped hazelnuts in a dry skillet over medium heat until fragrant (about 3-4 minutes). Toss with the finely chopped rosemary.
- Let the gratin rest for 10 minutes after removing it from the oven. Top generously with the toasted hazelnut/rosemary mixture and drizzle stripes of crème fraîche across the top before serving hot.