I don't usually follow a recipe when making a Potato Gratin. Use the following as a guideline and adjust everything to your own taste.
For a rich dish, use butter and whipping cream.
3 to 5 Russet Potatoes (or more depending on number of servings required)
1 garlic clove
1 teaspoon fresh thyme (optional)
Heavy Cream (or milk if you want a less rich version)
Gruyere cheese as well as cheddar and blue cheeses can be added for a different taste all together.
Salt and pepper
Rub cut garlic clove over the surface of a gratin or casserole dish. Butter.
Slice potatoes and place in pot and add enough cream/milk to almost cover. Add the garlic clove, thyme, salt and pepper. Bring to a boil and simmer for a few minutes, stirring often so the potatoes do not stick. When the potatoes have released some of their starch and thicken the liquid, remove the garlic clove, add 1 to 2 tablespoons butter and some grated Parmesan cheese. Pour into prepared casserole dish, dot with butter and sprinkle with some more Parmesan cheese. TIP: If you like a more garlicky flavour, just grated a garlic clove on a microplane and add to the cream mixture.
Bake in a 375°F oven for 45 to 55 minutes or until potatoes are tender. Remove from oven and let sit for 10 minutes before serving.
Another way to make a potato Gratin is to saute some thinly sliced onions in olive oil or butter until golden, add some thyme, and some chicken broth. Add the potatoes, salt and pepper and bring to a boil. Pour into a buttered casserole dish sprinkle with some Parmesan cheese and bake until cooked.