How to Make It
Preheat the oven to 300°. Set six 5- to 6-ounce ramekins or custard cups in a medium baking pan.
In a medium saucepan, combine the milk, lemon peel and cinnamon stick and bring to a boil. Remove from the heat and let stand for 15 minutes; discard the lemon peel and cinnamon stick pieces.
Meanwhile, in a small saucepan, cook 1/2 cup of the sugar with the water over moderately high heat, stirring just until the sugar dissolves. Lower the heat to moderate and let the sugar syrup simmer, without stirring, until a deep amber caramel forms, about 15 minutes. Immediately pour the caramel into the ramekins, tilting them as necessary to evenly coat the bottoms.
In a large bowl, whisk the eggs with the remaining 1/2 cup of sugar. Slowly whisk in the warm milk, then strain through a fine sieve into a large measuring cup or a bowl. Pour the custard into the ramekins. Pour enough hot water into the baking pan to reach halfway up the sides of the ramekins. Bake for about 40 minutes, until a knife inserted into a flan comes out clean. Transfer the ramekins to a rack and let the flans cool to room temperature. Refrigerate the flans for at least 4 hours or overnight.
To serve, run a thin knife around each flan. Top each flan with an inverted dessert plate and unmold, letting the caramel run over the flans. Serve at once.