Scalloped potatoes is a dish that is generally kept for special occasions. With a rich cream running through layers and layers of potatoes — and typically chock-full of cheese — it's definitely not something you eat when you're watching your diet.
If you are on a diet, here's a trick you can use. The trick is to swap half the heavy cream for chicken or vegetable stock. It's a small change that takes out hundreds of calories, but because cream is still in there, the reduction is not missed a bit. Caramelizing the onions for a few minutes really ups the sophistication of this dish, while the cheesiness of it all will bring all the comfort you'd expect.
Pro tip: To make a complete meal, add cooked ham as one of the layers in your scalloped potatoes!