To make au gratin potatoes its best to start with white, yellow, or red potatoes. Slice them about 1/8th of an inch thick, peeled or skin on is completely up to you, the peel of the potato contains nutrients so take this into consideration. Par cook the potatoes in water to help expedite cooking time. The water can be flavored with additional seasonings to give the potatoes more flavor if desired, ingredients like garlic, fresh herbs, peppercorns, and shallots can be added to the water, and water can even be subbed for chicken or vegetable stock. Once the potatoes are almost fully cooked, meaning they still have a little resistance to them, they should be drained well and arranged in a casserole dish or any heavy-bottomed pan. A flavorful cheese sauce or a sauce mornay should then be poured over the par-cooked potatoes and a sprinkling of shredded cheese on top of the potatoes before they are placed in the oven to finish cooking, will yield a beautiful golden-brown crust. The potatoes should bake at 350 F for 20-25 minutes until they are fork-tender and the cheese is melted and golden. Allow the gratin to cool for 5-10 minutes before serving. A sprinkling of flakey salt and some fresh herbs such as rosemary or thyme is an extra special touch.