Ingredients:

  • 3 lbs Starchy Potatoes (Russet or Maris Piper), peeled and thinly sliced
  • 2 large Garlic Cloves
  • 1 Tbsp Unsalted Butter
  • 1 small Shallot or Small Onion, finely minced
  • 3 cups Skimmed or Semi-Skimmed Milk
  • 1 cup Low-Sodium Chicken or Vegetable Stock
  • 1 Tbsp Cornflour (Cornstarch)
  • 2 Tbsp Cold Water (for cornflour slurry)
  • 1/2 tsp Freshly Grated Nutmeg
  • 2 tsp Kosher Salt, plus more for layering
  • 1/2 tsp White Pepper
  • 4 oz Reduced-Fat Mature Cheddar or Light Gruyère, grated
  • 1 tsp Fresh Thyme Leaves (optional, for garnish)

Instructions:

  1. Prepare the Oven and Dish: Preheat oven to 350°F (180°C). Rub the bottom and sides of the 9x13 inch baking dish thoroughly with one cut clove of garlic.
  2. Slice the Potatoes and Aromatics: Peel and slice the potatoes uniformly into 2mm thick discs (ideally using a mandoline). Finely mince the shallot and the remaining garlic clove.
  3. Sauté the Aromatics: Melt the butter in a saucepan over medium heat. Sauté the minced shallot until translucent (about 3 minutes). Add the minced garlic and cook for 1 minute until fragrant; do not brown the garlic.
  4. Combine Liquids and Thicken: Pour in the milk and stock and bring the mixture just to a gentle simmer. Whisk together the cornflour and 2 tablespoons of cold water to form a slurry. Slowly pour the slurry into the simmering milk mixture while continuously whisking vigorously.
  5. Finish the Sauce: Cook for 1–2 minutes until the sauce lightly coats the back of a spoon. Remove from heat and stir in the salt, white pepper, and nutmeg. The sauce should taste slightly over-seasoned at this stage.
  6. Layer the Gratin: Arrange the potato slices in the prepared dish in tight, overlapping rows. Pour approximately 1/3 of the sauce evenly over the first layer. Repeat this layering process twice more, ensuring the sauce is distributed throughout all layers.
  7. Bake (Covered): Sprinkle the grated reduced-fat cheese evenly over the top. Cover the dish tightly with foil. Bake for 50 minutes at 350°F (180°C) until the potatoes are tender when pierced.
  8. Bake (Uncovered): Remove the foil. Increase the oven temperature to 400°F (200°C). Bake for an additional 15–20 minutes, or until the top is golden brown and bubbling, and the sauce is fully set.
  9. Rest and Serve: Crucially, let the gratin rest for 15 minutes outside the oven before slicing and serving. Garnish with optional fresh thyme.