From the blog Kate's Kitchen, adapted from Everyday Food
"B" sized red potatoes (look for potatoes that are approximately the diameter of your muffin tin openings)
Freshly ground black pepper
Gruyere cheese, grated (can also use Romano or Parmesan)
Preheat oven to 400º. Grease muffin tins with butter or Pam.
Slice the potatoes thinly...a mandoline is very helpful, but it's also easily done with a knife. Lay two slices of potatoes in each muffin cup. Sprinkle with seasonings. Repeat with two more slices, and continue till cups are full. Add one tablespoon of cream to each gratin and top with cheese.
Bake for 30-35 minutes.