Preheat oven to 400°F. Grease 6×9 casserole loaf dish with butter.
Slice potatoes and onion into rounds. Mince garlic
Melt butter and stir in flour, salt, and pepper. Slowly add heavy cream and bring to boil. Simmer for 2 minutes until thick. Remove from heat and add cheese and combine until melted. Add potatoes, onions, and garlic
Cover with foil and cook for 50 minutes
Bump oven up to 425°F, remove foil and cook for 20 minutes. When tender, sprinkle with more cheese and cook for 10 minutes.