Ingredients
Equipment
Method
Prep and bake setup
- Preheat oven to 375F, then butter a 9x13-inch baking dish for easy release.
Make the creamy sauce
- Melt butter, then cook minced garlic for 30 seconds until fragrant, stirring and keeping it from browning.
- Whisk in all-purpose flour and cook for 1 minute to remove the raw flour taste, until smooth and lightly thickened.
- Slowly whisk in whole milk and heavy cream, then simmer until thickened, whisking often as it coats the back of a spoon.
- Season the sauce with salt, black pepper, and fresh thyme leaves, stirring to evenly distribute the herbs and specks.
- Remove from heat and stir in 1 cup cheddar and 1/2 cup Gruyere so they melt into a creamy, glossy sauce.
Layer and bake
- Layer a third of the sliced Yukon gold potatoes in the baking dish, spreading them into an even bed.
- Spoon a third of the sauce over the potatoes, letting it seep down between the slices.
- Repeat layering with another third of potatoes and another third of sauce, smoothing the top layer for even baking.
- Repeat once more with the remaining third of potatoes and the remaining third of sauce, then top with the remaining shredded cheddar and Gruyere.
- Cover with foil and bake for 45 minutes, until the potatoes look tender at the edges and bubbling begins under the foil.
- Uncover and bake 25-30 minutes more at 375F until golden and tender, with a bubbling cheese crust that has browned spots.
Rest and serve
- Rest for 15 minutes before serving so the layers set and the cheese sauce slices cleanly.
Notes
For the creamiest texture, slice potatoes consistently at about 1/8 inch so they bake at the same rate. Store leftovers covered in the refrigerator for up to 4 days; reheat in a 325F oven until warmed through. Freezing is not recommended because the dairy can separate after thawing. If you want a lighter option, use half-and-half instead of the heavy cream while keeping whole milk.