Ingredients:
- & Freshly Ground Black Pepper, to taste
Instructions:
- Preheat oven to 375°F (190°C). Lightly grease a 2-quart (or 9x13 inch) baking dish. Slice potatoes very thinly and uniformly (about 1/8 inch). Soak the slices in cold water for 15 minutes to remove excess starch, then drain thoroughly and pat completely dry.
- Make the Roux: In a large saucepan, melt the butter over medium heat. Whisk in the flour and cook for 1 minute until a smooth paste forms.
- Add Liquids: Slowly whisk in the warm milk, ensuring no lumps form. Continue whisking until the sauce thickens enough to coat the back of a spoon (about 5–7 minutes).
- Flavour & Finish: Reduce heat to low. Whisk in the heavy cream, minced garlic, nutmeg, and Dijon mustard. Season generously with salt and pepper. Remove from heat and stir in half of the grated Gruyère and Cheddar until fully melted and smooth. Keep warm.
- Assembly Start: Spread a thin layer of the cheese sauce across the bottom of the prepared baking dish. Arrange one layer of potato slices over the sauce, overlapping slightly. Sprinkle lightly with salt, pepper, and chopped parsley.
- Layering: Ladle about one-third of the remaining sauce evenly over the potatoes. Sprinkle with a light dusting of the reserved grated cheeses.
- Repeat the layering process (potatoes, sauce, cheese) two more times until all ingredients are used, ensuring the top layer is generously covered with the remaining sauce and cheese.
- Initial Bake (Covered): Cover the dish tightly with foil. Bake for 45 minutes to steam the potatoes through.
- Final Bake (Uncovered): Remove the foil. Bake for an additional 30–40 minutes, or until the top is deep golden brown, bubbling, and a knife inserted easily meets no resistance (potatoes are tender).
- Rest: Remove from the oven and let the Cheesy Au Gratin Potatoes rest for at least 15 minutes before slicing and serving. This allows the sauce to set properly.