2 tbsp chopped fresh parsley (optional, for garnish)
Instructions
Preheat oven to 375°F (190°C). Grease a 9x13-inch baking dish with butter or nonstick spray.
Place potato slices in a large bowl and cover with cold water; set aside.
In a large saucepan, melt 3 tablespoons butter over medium heat. Add onion and cook until softened, about 5 minutes. Add garlic and cook 1 minute more.
Stir in flour and cook for 1 minute, whisking constantly. Gradually whisk in milk and cream until smooth. Bring to a simmer, then reduce heat to low and cook, stirring occasionally, until thickened, about 5 minutes.
Remove from heat. Stir in salt, pepper, nutmeg, and 1 cup of the cheddar cheese until melted.
Drain potato slices and pat dry with paper towels. Layer half of the potatoes in the prepared baking dish. Pour half of the cream sauce over the potatoes. Repeat with remaining potatoes and sauce. Sprinkle remaining 1/2 cup cheddar cheese on top.
In a small bowl, melt remaining 1 tablespoon butter. Mix with panko breadcrumbs until coated. Sprinkle over the casserole.
Bake uncovered for 45-55 minutes, until potatoes are tender and top is golden and bubbly. Let rest for 10 minutes before serving. Garnish with parsley if desired.
Tips
For extra creamy texture, use Yukon Gold potatoes instead of russets.
Casserole can be assembled a day ahead; refrigerate and add 10 minutes to baking time.
Leftovers keep well in the refrigerator for up to 4 days; reheat in the oven or microwave.