Preheat your oven to 350 degrees. Grease a 9 x 13 casserole dish with unsalted salted butter.
Pour your heavy cream into a large measuring cup or bowl and add your salt, pepper, and garlic. Whisk it all together. Mix all your cheeses together in a separate bowl.
Place one layer of potatoes on the bottom of your casserole dish, top with half of the cheese. Add another layer of potatoes and the rest of the cheese. Now, finish the casserole with one more layer of potatoes and top with the cream mixture. Cover with foil and bake for 45 minutes. Take the foil off and bake for another 30-35 minutes until bubbly and brown. Take the casserole out of the oven and let it rest 10 minutes before serving. This is so decadent and delicious! Enjoy!