Can I pre-prepare dauphinoise potatoes? I am hosting my first Christmas for the mother-in-law so of course am freaking out.

I'm planning on cooking a roast something but with a slightly different spin on it from normal Christmas Dinner as it'll be on the 27th so I thought of making something different. 

I thought dauphinoise potatoes would go down a treat. I haven't made them before but the recipe seems fairly straightforward. My question is how much prep can I do the day before? As I'm keen to have a few dishes ready and on trays to go in the oven without needing lots of morning prep. 

Can I pre-slice the potatoes? Will they keep in water in the fridge? 

I have seen some recipes which include cream, garlic and gruyere. I'm guessing these ingredients need to be cooked off immediately prior and cannot be made up beforehand.
You can make it days in advance and freeze it.

Bake it as the recipe says, then cover with aluminum foil and plastic wrap and freeze it as quickly as possible (that it the most important factor)

On christmas day, get it out of the freezer, pop it in the oven and serve when really hot.