Grease a fry pot with a capacity of about 1 liter with butter.
Turn on the oven to preheat to 180 degrees. Place the potato slices in one layer in an oiled roasting pan. Sprinkle potatoes with half garlic, half red onion, and 1/3 cheese. Season with salt and pepper.
Repeat layers, ending with potatoes sprinkled with cheese.
Pour the cream over the contents of the brazier and place in the preheated oven. Bake the potatoes for about 1.5 hours, until the top is golden brown. Serve the potatoes immediately, directly in the broiler.