Infuse the cream with sage and smashed garlic, then season with salt and pepper
Bring the cream mixture to a simmer, then reduce to lowest heat for 5 minutes
Turn off heat and let the cream mixture sit for 10 minutes
Thinly slice the potatoes
In a 2 qt baking dish, layer the sliced potatoes with infused cream and parmesan cheese, repeating until all potatoes are used
Finish the top layer with remaining cream and parmesan, then dot with butter pieces
Cover the dish tightly with parchment paper and foil
Bake covered at 375°F for 1 hour
Uncover and sprinkle shredded Gruyere or cheddar cheese on top
Bake uncovered for 20-30 minutes until golden and bubbly
Let sit for 20 minutes before serving
