Ingredients:
- 3 lbs Russet or Yukon Gold Potatoes, peeled
- 4 Tbsp Unsalted Butter
- 4 Tbsp All-Purpose Flour
- 3 cups Whole Milk, warmed
- 1 cup Heavy Cream
- 1 cup packed Sharp Cheddar Cheese, divided
- 1/2 cup Grated Gruyère or Smoked Gouda
- 1 tsp Fresh Thyme Leaves
- 1 clove Garlic, finely minced
- Pinch Freshly Grated Nutmeg
- Salt and freshly ground Black Pepper, to taste
Instructions:
- Preheat oven to 375°F (190°C). Grease a 9x13 inch baking dish thoroughly. Peel potatoes and slice them very thinly (about 1/8 inch or 3mm thick). Rinse the slices in cold water to remove excess starch, then thoroughly pat dry.
- Lightly sauté the minced garlic and thyme in 1 tablespoon of butter until fragrant (about 1 minute). Set aside.
- Melt the remaining butter in a large saucepan over medium heat. Whisk in the flour to form a smooth paste (the roux). Cook for 1-2 minutes until the raw flour smell disappears.
- Gradually whisk in the warm milk, ensuring no lumps form. Bring the mixture to a gentle simmer, whisking constantly, until the sauce thickens enough to coat the back of a spoon.
- Remove the pan from the heat. Whisk in the heavy cream, nutmeg, salt, and pepper. Stir in 3/4 cup of the Cheddar and all of the Gruyère/Gouda until melted and smooth. Stir in the sautéed garlic/thyme mixture.
- Arrange a single, slightly overlapping layer of potato slices in the prepared baking dish. Season lightly with salt and pepper. Repeat this layering process until all potatoes are used.
- Slowly pour the cream sauce evenly over the stacked potatoes, gently shaking the dish to help the liquid seep down.
- Cover the dish tightly with aluminium foil. Bake for 45 minutes.
- Remove the foil. Sprinkle the remaining 1/4 cup of Cheddar evenly over the top. Return the dish to the oven (uncovered) and bake for another 15–30 minutes, until the top is deeply golden brown and the potatoes are completely tender.
- Let the gratin rest on a cooling rack for 10–15 minutes before slicing and serving.