• 3 tbsp. unsalted butter
• 3 c. whole milk or half-and-half
• 2 tbsp. finely chopped parsley, for garnish
Preheat oven to 350 degrees. Spray a 9- by 13-inch ovenproof casserole dish with olive oil. Combine the garlic, flour, salt and pepper together in a small bowl and mix to combine.
Arrange 1/3 of the potatoes on the bottom of the dish and then sprinkle with half of the onions. Sprinkle half of the flour mixture on the onions. Sprinkle with 1/3 cup of grated cheese. Dot with 1 tablespoon of butter. Make another layer exactly the same way. Layer with the last third of the potatoes, the last third of the cheese and dot with the remaining tablespoon of butter. Pour over the milk or half and half and cover with foil. Place the casserole on a baking sheet.