This is my 'go-to' gratin for potatoes... Patricia Well's Gratin Dauphinois. Very easy and just terrific:
1 garlic clove, halved
2 pds. potatoes, peeled and sliced thin
4 oz. swiss cheese grated (Gruyere, ideally)
2 cups milk
1/2 cup cream
preheat oven to 375
rub the inside of baking dish with garlic
combine potatoes, 3/4 of cheese, milk cream, salt and pepper in a large bowl. Mix well. Spoon into baking dish, pouring the liquid over potatoes. Cover with remaining cheese.
Place in oven and bake about 1 hr. 15 minutes.
It is as easy as that. If you want to take 5 minutes and be a little more fancy, you can arrange the potatoes in layers and then press them down for about 30 minutes with a plate topped with canned goods. Either way, they are terrific.
This is simple and it works:
Pre heat oven to about 375F (if you are roasting something else at say 400 then that would be fine)
Peel and thinly slice as many potatoes as you need (I use 1 fist sized per person), waxy verieties work best. Place them in a saucepan.
Just about cover with a 50/50 mix of whole milk and heavy cream, well seasoned with salt and pepper. Bring this up to simmering point with a bit of stirring. Add some grated nutmeg if you like.
Spoon the hot mixture into a suitable baking/gratin dish (you could wipe a cut clove of garlic round the inside of the dish first), and into the oven with it until the top is golden brown. Probably about 45 minutes.
If you want the cheesy version, which would be nice with your ham, then add a handfull of grated Gruyere (or similar) into the pre-heat stage, and sprinkle some more over prior to baking.
This is pretty much taken from the great Roux brothers, who have continuously held 3 Michelin stars here in the UK for over 25 years
Edit: This re-heats well (cool, cover and fridge it, of course) 24 hours later.
I don think you need a complicated recipe really.
Potatoes, cream, cheese...
I like romano, pecorino, and parmesan.
Add some very thinly slice onions, chop up some roasted garlic, salt and pepper.
Grease your pan and roast till tender -make sure to top with some bread crumbs and more cheese.