Ingredients
Equipment
Method
- Preheat the oven to 375°F.
- Coat a 9x13-inch baking dish with nonstick cooking spray.
Make the sauce
- Melt the butter in a medium saucepan over medium heat.
- Add the garlic and cook for 30 seconds.
- Whisk in the flour and cook for 1 minute.
- Gradually whisk in the milk and heavy cream, bring to a gentle simmer, and cook, stirring, for 3 to 5 minutes, until the sauce thickens enough to coat a spoon.
- Remove the pan from the heat and stir in the salt, pepper, and thyme.
Assemble and bake
- Arrange the sliced potatoes in three even layers in the prepared dish, spreading sauce over each layer and sprinkling 2 ounces of Gruyere between the first and second layers and between the second and third layers.
- Pour any remaining sauce over the top and scatter the remaining 4 ounces of cheese over it.
- Cover the dish tightly with foil and bake for 50 minutes.
- Remove the foil and bake for 25 to 35 minutes, until the top is golden and a knife slides easily into the potatoes.
- Let the potatoes rest for 15 minutes before serving.
Notes
For even cooking, slice the potatoes uniformly. Refrigerate leftovers for up to 4 days; freezing is not recommended because the potatoes can become grainy. For a gluten-free version, use a gluten-free all-purpose flour blend.
