Preheat oven to 400ºF.

Prepare potatoes:

• Pat the sliced potatoes dry with paper towels and then toss the potatoes with salt, pepper, ground nutmeg, and 1 tablespoon of truffle oil. Set aside.

Prepare the béchamel:

• Add the cream to a small saucepan and turn the heat to low. Set aside. In a large saucepan, melt the butter over medium heat. Add the flour and stir to incorporate.
• Cook for 1-2 minutes until golden, but not overly browned. Whisk in the warm heavy cream and continue whisking until smooth. Bring the mixture to a very low boil and immediately turn the heat to low.
• Continue whisking as the sauce thickens. Cook for 2-3 more minutes or until the sauce reaches your desired consistency. Taste and season with salt and white pepper.
• Sprinkle in the nutmeg and truffle zest and whisk to incorporate. Remove from heat.

Prepare the casserole:

• Grease the bottom and inside of a large casserole dish. Arrange a layer of overlapping potatoes along the bottom of the dish. Drizzle a teaspoon of truffle oil on top of the potato layer, if desired.
• Spoon a ladle or two of the béchamel on top and use the back of the ladle to evenly spread the sauce on top of the potatoes. Continue layering with potatoes, truffle oil (optional), and the béchamel until no ingredients remain. Note: You should end the dish with a thin layer of béchamel on top of the casserole.

Bake the gratin:

• Cover the casserole dish with foil and transfer to the oven. Bake for 1 hour. After 1 hour has passed, remove the foil and bake for an additional 20 minutes or until the top of the casserole is golden. Sprinkle the casserole with fresh thyme leaves if desired and let stand for 10-15 minutes before serving.

To serve:

• Serve the casserole family style. Enjoy!