1. This recipe will work great with any potato other than the really waxy ones used for potato salads (usually red potatoes). I just use the dirt brushed Sebago potatoes which are the most common ones here in Australia and are a great all rounder. US: Russet and Yukon Gold will both be great.
Waxy potatoes aren't great for this recipe because they retain their shape and firmness too well. You want the potatoes to go soft and breakdown inside so it mingles with that creamy sauce when you bite into it!
2. I like using a touch of mayo in this because it adds a bit of extra flavour. Mayo haters can skip it and use a bit more cream, but I'd add a bit of seasonings as well eg. 1/4 tsp each mustard powder and onion and/or garlic powder.
3. Cheese - this really can be made with any cheese that melts well (i.e. not feta, goats cheese). I choose to mix through a flavoured cheese, like Gruyere (my absolute favourite, but a bit expensive), Monterey Jack, Colby, cheddar, tasty cheese (very common and good value everyday cheese here in Australia, tastes a bit like like Colby). Then I top it with mozzarella because I like how it browns so nicely without leaving pools of oil.
4. When you pull it out of the oven after the covered bake time, you'll notice that the liquid looks split. That's just the reality of cream when it's cooked for a long period of time like this. But by the end of the baking time and after it is rested, the sauce is reduced so that you can't really see it anyway. The same thing happens when you make a classic French Potato Dauphinoise, it can't be avoided. It does not affect taste or texture when you eat it. It's just the way things are! :)
5. REHEATING: Reheats really well, probably even better than scalloped potatoes / potato gratin
because it's saucier. Allow to cool, then refrigerate covered. Because it's quite dense, it takes a while to reheat in the oven so I recommend microwaving (also keeps it more moist). About 10 minutes on medium should do the trick.
BEST MAKE AHEAD OPTION: Bake until potatoes are tender, take out of oven, cover and cool, refrigerate. Then either cover and microwave to reheat (5 - 8 minutes) or bake at 180C/350F for 20 - 30 minutes, THEN scatter with cheese and bake uncovered until cheese is golden.
6. Nutrition assumes 10 servings.