Preheat oven to 425 degrees.
1. Liberally butter the bottom of a rectangular baking dish with half of the butter and set aside.
2. Place a small saucepan with the milk, garlic, salt, pepper, and nutmeg over low heat while you set about peeling and slicing the potatoes. A mandoline is perfect for this, but I usually opt for a really sharp butcher knife, mostly because I'm too lazy to drag out and wash any extra equipment.
3. Slice the potatoes about an eighth of an inch thick, discarding the smallest slices. Don't wash the potatoes after slicing them the surface starch is indispensable.
4. Evenly arrange the potatoes in the bottom of the baking pan, one overlapping row at a time.
5. Layer the following row about a third of the way over the previous row. Alternate rows of sweet and Yukon gold potatoes.
6. Continue until the baking pan is neatly paved. It should look something like a shingled rooftop.
7. Bring the milk to a boil, fish out the garlic clove, and pour the milk over the potatoes.
8. Cover the pan with aluminum foil and bake in the middle of the oven for about 15 minutes until most of the milk has been absorbed.
9. Meanwhile, set the cream over low heat and bring to a boil.
10. Pour the cream over the semi-cooked potatoes and dot the entire surface with the remaining butter.
11. Continue to bake, uncovered, for another 20 to 25 minutes until the potatoes are golden brown and spotted with darker, crisp areas.
12. The potatoes will be dotted with thickened cream, especially between the slices. Allow the gratin to rest for 10 minutes before serving.
The KitchenAid Candy Apple Red Food Processor can be purchased at: www.kitchenaid.com.
Get David's book and other recipes here: www.chefdavidlawrence.com.