How to Make It
Preheat the oven to 300°. Sift the brown sugar into a small baking dish or a pie plate. Bake the sugar for about 18 minutes, or until dry. Transfer to a plate and set aside. Keep the oven on.
In a saucepan, combine the milk with the cream, sugar, citrus zests and cinnamon stick and bring to a simmer over moderate heat. Remove from the heat.
In a medium bowl, lightly beat the egg yolks. Whisk in 1/2 cup of the infused milk, then whisk the yolk mixture into the remaining infused milk in the saucepan. Strain the custard and pour it into two 3/4- or 1-cup ramekins.
Set the ramekins in a small baking dish and add enough hot water to the dish to reach halfway up the side of the ramekins. Bake for about 45 minutes, or until the custards are barely set. Remove the ramekins from the baking dish, let cool slightly and cover loosely with foil. Refrigerate the custards until chilled, at least 2 hours.
Preheat the broiler. Set the ramekins in a shallow baking dish packed with ice. Sprinkle the brown sugar evenly over the custards and broil 4 inches from the heat until golden brown, about 15 seconds; shift the baking dish for even browning. Serve at once.