When making scalloped potatoes, there are a few tips that can make the process much easier and help ensure a more consistent dish. The potatoes need to be sliced to the same thickness for even cooking. A long baking time is typically necessary to ensure the potatoes are cooked through both thoroughly and evenly, though parboiling them before baking can reduce this. It is often best to reserve some cheese until the dish is just about done, and then to top it at the end to allow the cheese to melt and brown without burning.
One of the most important considerations in making scalloped potatoes is the thickness and doneness of the potatoes themselves. Even thickness for slices is vital to ensure that each piece cooks at the same rate as every other one. This ensures that all of the potatoes in the dish will be done at the same time, which is important as otherwise some pieces may be perfectly cooked while others are underdone. Using a mandolin to make scalloped potatoes can greatly simplify this, as the set blade ensures even slicing of each piece.
Scalloped potatoes need an adequate amount of time in an oven to ensure that they are properly cooked through, even with consistent thicknesses. This often requires a fairly long bake time, with the potatoes covered in a milky, cheesy sauce that cooks them. Shorter baking times can be achieved by first parboiling the potato slices in a pot of water, either completely cooking them or getting them very close to being done. The scalloped potatoes can then be assembled and baked in an oven to allow the flavors to mingle, but less time is required to get the potatoes cooked properly.
This long baking time can make scalloped potatoes fairly easy to burn, yet they are typically baked uncovered to help ensure even and precise cooking temperatures. Leaving them uncovered is also important since it keeps the sauce thick and creamy; covering the dish would trap steam and potentially water it down. As the baking time comes to an end, however, it can be helpful to sprinkle some shredded cheese over the top of the scalloped potatoes and then to put them under a broiler. This applies direct, powerful heat to the top of the dish, which melts and browns the cheese, but can be done for a short time to prevent burning.