Preparation

• Position a rack in the center of the oven and heat the oven to 350°F. Butter a 9×13-inch (or similar) baking dish.
• In a 5-quart pot, bring the milk, cream, nutmeg, and garlic to a boil over medium-high heat. Reduce the heat to medium low and simmer 5 minutes, stirring occasionally, to infuse.
• Meanwhile, melt the butter and pour into a medium bowl. Add the breadcrumbs and Gruyère and toss.
• Stir the potatoes, 1-1/2 Tbs. salt, and 1/2 tsp. pepper into the milk mixture, raise the heat to medium high, and return just to a boil. Carefully transfer the potato mixture to the prepared dish and spread out evenly. Scatter the breadcrumb mixture over the top and bake until the potatoes are tender when pierced with a fork, and the breadcrumbs are golden-brown, about 45 minutes.
• Let rest 15 minutes before serving.

• For a sweeter gratin, substitute sweet potatoes for half of the potatoes.
• Instead of infusing the cream with nutmeg and garlic, whisk in 1 to 2 Tbs. of adobo (from a can of chipotles in adobo) for a little heat.
• Make it extra cheesy: Put half of the potato mixture in the casserole dish, then add an extra cup of Gruyère before adding the rest of the potatoes and the topping.