Cheesy Au Gratin Potatoes
Three-cheese au gratin potatoes with a homemade cheese sauce and caramelized onions - rich, creamy, and perfect for holiday dinners or any time you need an impressive side dish.
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Servings: 10
Ingredients
- 3 lbs Yukon gold potatoes 6-7 medium, sliced 1/8-inch thick
- 1/2 yellow or white onion thinly sliced
For the Cheese Sauce:
- 2 Tbsp salted butter
- 1/4 cup all-purpose flour
- 1½ cups whole milk
- 8 oz sharp cheddar cheese shredded (2 heaping cups)
- 3/4 tsp salt plus more to taste
- 1/2 tsp garlic powder
- Freshly ground black pepper to taste
For Topping:
- 1/2 cup shredded gruyere cheese or substitute more sharp cheddar
- 1/4 cup grated parmesan cheese
- Fresh chopped parsley for garnish optional
Instructions
- Preheat oven to 375°F. Grease a 9x13-inch baking dish with butter or cooking spray.
- Arrange sliced potatoes in three slanted rows in the prepared dish. Potatoes should overlap slightly but not be packed too tightly. Tuck onion slices throughout between and on top of potato layers.
- Make cheese sauce: Melt butter in medium saucepan over medium heat. Gradually whisk in flour and milk, alternating small amounts and whisking constantly to prevent lumps. Continue until all flour and milk are incorporated.
- Bring mixture to a simmer, stirring frequently, until thickened to gravy consistency.
- Reduce heat to low. Stir in shredded cheddar, garlic powder, salt, and pepper until cheese is fully melted. Taste and adjust seasoning as needed.
- Pour cheese sauce evenly over potatoes and onions, making sure sauce reaches all corners of dish.
- Cover pan tightly with aluminum foil. Bake 45 minutes.
- Remove foil and sprinkle gruyere and parmesan evenly over top. Return to oven uncovered.
- Bake additional 30-45 minutes until potatoes are fork-tender in the center and top is golden brown with crispy cheese spots.
- Let rest 10 minutes before serving. Garnish with fresh parsley if desired.
Notes
- A mandolin makes quick, even work of slicing potatoes
- Use freshly shredded cheese for best melting - pre-shredded contains anti-caking agents
- Sharp cheddar is important for flavor - don't use mild
- Make ahead: Assemble completely, cover with foil, and refrigerate up to 3 days.
- Add 15-20 minutes to baking time when cooking from cold
- Add cooked, crumbled bacon (6-8 oz) for extra richness
- Leftovers keep refrigerated 5 days; reheat in microwave or 350°F oven
- Potatoes are done when fork easily pierces through center layers