We usually have these on Christmas, and they are so decadent.

Ingredients
2 pounds Yukon gold potatoes, peeled and sliced into ¼ in slices
1 clove garlic
1 onion sliced thin
½ tablespoon live oil
6 tablespoons butter
1 cup cream
S and P to taste
2 and ½ cups shredded swiss, cheddar, or favorite cheese or a combination

Instructions
Place sliced potatoes into a pot, cover with water and bring to a boil
Immediately turn off heat
Remove pot from burner and let sit for 5 minutes
Drain well
Preheat oven to 425 degrees, smash the garlic and rub a 13×9 dish with it, then butter and set aside
Heat the remaining butter with the cream until butter is melted and the cream hot
Heat the olive oil over medium heat and sauté the onion until soft, not browned
Divide the cheese into thirds
Layer ¼ of the onion in the bottom of the baking dish. Add ½ of the potatoes on top of the onion
Split the remaining onion in half and set aside
Sprinkle the potatoes with Sand P, 1/2 the onion, and 1/3 of the cheese
Add the remaining potatoes,  season again with S and P and add the remaining onions and 1/3 of the cheese
Reserve the last 1/3 of the cheese for the last few minutes of cooking when you will return the dish to the oven for 5 minutes until the cheese begins to brown
Pour the hot cream mixture over top of the casserole and bake at 425 until potatoes are soft
Add remaining cheese (above note) and bake another 5 minutes until cheese begins to brown