2 tablespoons unsalted butter
1 medium onion, minced (about 1 cup)
1¼ teaspoons salt
¼ teaspoon pepper
2½ pounds russet potatoes (about 5 medium), peeled and sliced 1/8-inch thick
2 cups milk – heated
4 ounces grated cheddar cheese or more, shredded (1 cup or more)
Panko breadcrumbs to top
- In a food processor fitted with an ⅛-inch (~3mm) slicing blade, slice potatoes or slice by hand
- Melt butter in large Dutch oven and add onion and cook, stirring occasionally, until soft and lightly browned, about 4 minutes.
- Add potatoes, milk, and salt and pepper, and bring to simmer.
- Cover, reduce heat to medium-low, and simmer until potatoes are almost tender (about 10 minutes)
- Transfer mixture to baking dish.
- Adjust oven rack to middle position; heat oven to 425°.
- Sprinkle evenly with cheese and top with bread crumbs.
- Bake until milk is bubbling around edges and top is golden brown, 15 – 30 minutes. Cool 10 minutes before serving.
To Make Ahead:
Once the scalloped potatoes have been transferred to the baking dish and pressed into an even layer, they can be wrapped in plastic wrap and refrigerated for up to 24 hours. When ready to bake, add the cheese, cover with foil, and bake in a 400-degree oven until the mixture is hot and bubbling, about 45 minutes. Remove the foil and cook until the cheddar begins to brown, about 30 minutes longer. Let cool for 10 minutes before serving.