Ingredients
Equipment
Method
Preheat and prepare the baking dish
- Preheat the oven to 375F, then butter a 9x13-inch baking dish so the potatoes release easily after baking.
Make the creamy garlic sauce
- Melt the butter in a saucepan over medium heat, then cook the minced garlic for 30 seconds, stirring until fragrant.
- Whisk in the all-purpose flour and cook for 1 minute to remove the raw flour taste.
- Slowly whisk in the whole milk and heavy cream, then simmer until the mixture thickens enough to coat the back of a spoon.
- Season the thickened sauce with salt, black pepper, and fresh thyme leaves, then remove the pan from heat.
- Stir in 1 cup shredded sharp cheddar and 1/2 cup shredded Gruyere until fully melted and smooth.
Layer, bake, and brown the top
- Layer a third of the potato slices in the baking dish, then spoon over a third of the sauce; repeat twice, ensuring the final layer is potatoes.
- Top with the remaining cheese by sprinkling the reserved cheddar and Gruyere evenly over the surface.
- Cover tightly with foil and bake at 375F for 45 minutes, using a visual cue that the potatoes look softened at the edges.
- Uncover and bake 25 to 30 minutes until golden and tender, watching for a bubbling cheese crust and browned top spots.
Rest and serve
- Rest for 15 minutes before serving so the layers set and slice cleanly.
Notes
For the smoothest, scoopable slices, slice potatoes to a consistent 1/8 inch thickness so everything cooks evenly in the same bake time. Refrigerate leftovers in a sealed container for up to 4 days; reheat covered at 325F until hot throughout. Freezing is not recommended because the creamy sauce can break after thawing. Dietary swap: use lactose-free whole milk and lactose-free cream for a similar texture without lactose.