Scale

2.5 lbs Yukon Gold potatoes, peeled and thinly sliced

1 medium yellow onion, finely diced

4 tbsp butter

4 tbsp all-purpose flour

3 cups whole milk

1 cup heavy cream

1/2 tsp nutmeg

Salt and pepper to taste

1 cup shredded Gruyere cheese (optional)

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Preheat oven to 375°F (190°C). Grease a 9×13 inch baking dish.

Melt butter in a saucepan over medium heat. Add diced onion and cook until softened, about 5 minutes.

Stir in flour and cook for 1 minute, creating a roux.

Gradually whisk in milk and heavy cream until smooth. Bring to a simmer, stirring constantly.

Reduce heat and simmer for 5-7 minutes, or until the sauce has thickened slightly.

Season with nutmeg, salt, and pepper to taste.

Layer half of the sliced potatoes in the prepared baking dish. Pour half of the sauce over the potatoes, ensuring they are evenly coated.

Repeat the layers with the remaining potatoes and sauce.

Bake for 45 minutes. If using cheese, sprinkle it over the top during the last 15 minutes of baking.

Bake until the potatoes are tender and the sauce is bubbly and golden brown, about 10-15 minutes more.

Let stand for 10-15 minutes before serving.