Ingredients:

  • 3 lbs Russet (or Maris Piper) Potatoes, peeled and sliced 1/8 inch thick
  • 1 lb Yukon Gold (or Désirée) Potatoes, peeled and sliced 1/8 inch thick
  • 3 Tbsp Unsalted Butter
  • 3 Tbsp All-Purpose Flour
  • 2 cups Heavy Cream (Double Cream)
  • 2 cups Whole Milk
  • 2 cloves Garlic, smashed, left whole
  • 1 Bay Leaf
  • 1/4 tsp Fresh Nutmeg, freshly grated
  • 2 tsp Kosher Salt, plus more for layering
  • 1/2 tsp Freshly Ground Black Pepper, plus more for layering
  • 4 oz Gruyère Cheese, shredded
  • 2 oz Sharp White Cheddar, shredded

Instructions:

  1. Preheat the oven to 375°F (190°C). Grease a 9x13 inch baking dish lightly with butter. Peel all potatoes and slice them uniformly thin (about 1/8 inch or 3 mm). Briefly rinse the slices in cold water to remove excess starch, then thoroughly pat them dry with a clean tea towel.
  2. In a saucepan, combine the heavy cream, whole milk, smashed garlic cloves, and bay leaf. Heat gently over medium-low heat until small bubbles form around the edge (do not boil). Remove from heat, cover, and let infuse for 10 minutes. Remove and discard the garlic and bay leaf.
  3. In the same saucepan, melt the 3 Tbsp butter over medium heat. Whisk in the flour and cook for 1 minute until a pale roux forms. Slowly pour the warm, infused milk/cream mixture into the roux while whisking constantly. Bring the sauce to a gentle simmer, whisking occasionally until it thickens slightly (it should coat the back of a spoon).
  4. Remove the sauce from heat and stir in the nutmeg, 2 tsp salt, and 1/2 tsp pepper. Taste and adjust seasoning as needed—the sauce should be slightly salty now.
  5. Pour about one cup of the cream sauce into the prepared baking dish and spread evenly. Arrange half of the dried potato slices in overlapping, slightly angled rows across the dish. Season generously with extra salt and pepper.
  6. Pour about half of the remaining sauce over the potatoes. Sprinkle with half of the shredded cheese mixture (Gruyère and Cheddar). Add the remaining potato slices, arranging them neatly. Pour the rest of the cream sauce evenly over the top, ensuring the potatoes are mostly submerged.
  7. Cover the dish tightly with foil and bake for 60 minutes. The potatoes should be fork-tender but not mushy.
  8. Remove the foil. Sprinkle the remaining cheese mixture over the top. Return to the oven and bake uncovered for 15-20 minutes, or until the cheese is melted, bubbly, and deeply golden brown.
  9. Remove the gratin from the oven and crucially, let it rest for 10-15 minutes before scooping and serving. This allows the sauce and layers to properly set.