– Milk- Full fat is ideal to create a rich, creamy flavor and texture. – Onion- Roughly chopped to add extra texture to this dish. – Garlic- Peel it and slice it as finely as possible. – Fresh Thyme- Fresh will give a more intense flavor than dried. – Kosher Salt – Ground Black Pepper – Russet potato- Peeled and very thinly sliced for consistent cooking. – Sweet potato- These should be peeled and sliced to the same thickness as the russet potatoes. – Shredded cheese- A mixture of Swiss and Mozzarella is my favorite, but use whatever your preference may be. – Grated Parmesan Cheese- Helps to create the crispy, brown layer on top of the cheesy potato casserole.