Low-fat Cheddar cheese is big on flavor and low on caloric impact. Creamy and rich, this potato au gratin side dish won’t taste like diet food.
Preheat the oven to 350 degrees.
Coat a 9-by-13-inch glass baking dish with cooking spray. Generously coat a large pot with cooking spray and heat over medium heat. When hot, melt the butter. Add the onion to the pot and cook, stirring occasionally, until the onion starts to turn translucent and caramelize, about 10 minutes.
Add the potatoes, salt, pepper, nutmeg, milk, and cheese to the pot. Toss several times to coat each slice of potato. Bring to a boil and cook, stirring occasionally, until the sauce thickens enough to coat the back of a spoon, about 5 minutes.
Pour potato mixture into the baking dish and bake until the top is golden and potatoes are tender, about 45-60 minutes. Slice into 8 pieces and serve.