Ingredients
Equipment
Method
Prep the dish and preheat
- Preheat oven to 375F, then butter a 9x13-inch baking dish.
Make the creamy sauce
- Melt butter, cook garlic for 30 seconds, then whisk in flour for 1 minute.
- Gradually whisk in milk and cream, then simmer until slightly thickened.
- Season the sauce with salt, black pepper, and thyme.
Layer and bake
- Layer potatoes and onion in the dish in three layers, pouring sauce over each layer.
- Cover with foil and bake for 1 hour.
- Uncover, sprinkle with Parmesan, and bake 25 to 30 minutes until golden and fork-tender.
Rest and serve
- Rest 15 minutes before serving so the layers set and the sauce thickens.
Notes
For the most even tenderness, keep potato slices close to 1/8 inch and layer without compressing. Refrigerate covered up to 4 days; reheat in a 325F oven until hot throughout, or microwave individual portions. Freeze baked leftovers up to 2 months; thaw overnight in the fridge before reheating. For a lighter option, use evaporated milk plus reduced-fat cream cheese-based sauce instead of whole milk and heavy cream, keeping the simmering step to thicken.
