Heat the oven to 300°F and arrange a rack in the middle. Bring the water to a simmer in a medium saucepan over high heat; keep at a simmer.
Combine the eggnog, cream, milk, and nutmeg in a medium saucepan and bring to a simmer over medium heat. Meanwhile, whisk together the egg yolks and 1/3 cup of the granulated sugar in a medium bowl until pale yellow and thick, about 3 minutes.
While whisking constantly, slowly pour the heated eggnog mixture into the yolks in a steady stream. Once combined, divide the mixture among 6 (4-ounce) ramekins and place in a 13-by-9-inch baking dish. Pour the hot water between the ramekins until it reaches two-thirds of the way up the sides (you may not need all of the water). Cover the baking dish with aluminum foil and poke a few holes in it with a skewer or knife to allow steam to escape.
Bake until the centers of the custards are just set, about 30 to 35 minutes. Remove from the oven and transfer the custards to a wire rack to cool to room temperature, about 30 minutes. Cover the ramekins with plastic wrap and refrigerate until completely chilled, about 1 hour.
When ready to serve, heat the broiler to high and arrange a rack in the upper third. Place the custards on a baking sheet and sprinkle about 2 teaspoons of the remaining 1/4 cup sugar evenly over each. Place under the broiler until the sugar is caramelized and golden brown, about 1 to 2 minutes—watch carefully to avoid burning. (Alternatively, you can use a kitchen torch.) Serve immediately.
Beverage pairing:Badia di Morrona Vin Santo, Italy. Vin Santo, the classic sweet wine from Italy, is made from drying white grapes in the sun so the sugars get highly concentrated. It browns as it ages, giving it richness and positioning it between a white wine and a dessert wine. That tension between lightness and heavy sweetness makes it a good counterpart for this burnt, fresh, and spiced crème brûlée.