Peel and slice the potatoes thinly.
Make a white sauce by melting the butter in a saucepan, then whisking in the flour to make a roux.
Gradually whisk in the milk and cream, and cook until thickened.
Season the white sauce with salt and pepper.
Layer the potato slices and white sauce in a baking dish, topping with cheese.
Bake at 375°F until the potatoes are tender and the top is golden brown.
