Scalloped Potatoes

Preheat the oven to 375 °F (190 °C). Butter a 9×13-inch baking dish and set aside.

Slice the 2 ½ lb russet potatoes into ⅛-inch rounds using a mandoline or sharp knife. Keep them uniform so they cook evenly — thicker slices will stay underdone in the center.

Melt the 3 tbsp unsalted butter in a medium saucepan over medium heat. Add the 1 medium yellow onion and cook, stirring occasionally, for 4–5 minutes until softened.

Add the 3 cloves garlic and cook for 1 minute until fragrant.

Sprinkle in the 3 tbsp all-purpose flour and stir constantly for 1–2 minutes to cook out the raw flour taste.

Gradually whisk in the 2 cups whole milk and 1 cup heavy cream, pouring in a slow, steady stream to prevent lumps.

Season the sauce with 1 tsp kosher salt, ½ tsp black pepper, and ¼ tsp ground nutmeg. Bring to a gentle simmer, stirring often, and cook for 3–4 minutes until the sauce thickens enough to coat the back of a spoon.

Remove from heat and stir in ½ cup of the shredded Gruyère until melted.

Arrange half the potato slices in overlapping layers in the prepared baking dish. Pour half the cream sauce evenly over the potatoes.

Layer the remaining potato slices on top, then pour over the rest of the cream sauce, making sure it seeps down into the layers.

Scatter the remaining ½ cup shredded Gruyère evenly over the top.

Cover tightly with foil and bake for 45 minutes. Remove the foil and bake for an additional 25–30 minutes until the top is deep golden brown and a knife slides through the potatoes with no resistance.

Let the dish rest for 10 minutes before serving — this allows the sauce to set so it slices cleanly rather than running.