i used to make these about twice a week as my (then) young diabetic son was hooked on them, so i got used to doing a dish full very quckly. here's what i did:
peel and fairly thinly slice potatoes - i used to use the waxy red skinned ones.
layer them into an ovenproof dish putting some salt and some garlic granules in each layer.
almost cover with skimmed milk, dot with butter if you want (i never did) and bake for maybe an hour on a medium heat.
to make it richer for a special occasion i'd use half single cream and half milk.
sometimes i'd put some grated cheese in the layers and a sprinkling on top.
sometimes i'd use stock instead of milk.
some recipes say to rinse the sliced potatoes and pat them dry, i never did to save time.
my neighbour used to put sliced tomatoes in the layers. you can put what you like really, just depends what you like yourself. by far the nicest is the naughty version with cream and butter :)