Combine milk, cinnamon sticks, and sugar in a saucepan and, stirring, bring to a boil.
Cover and chill overnight.
Set 4 small baking dishes (each at least 2/3 cup size) in a baking pan and surround with hottest tap water to about half the depth of the dishes.
Remove dishes, put the pan of water in the oven, and set the oven temperature at 350°.
When oven has reached that temperature, again heat the milk mixture to scalding, stirring.
Set cinnamon aside and beat hot milk into the eggs with a fork.
Pour an equal portion of mixture into each baking dish and set the dishes in the hot water bath.
Bake at 350° for 25 to 30 minutes, or until the centers of the custards jiggle only slightly when a dish is shaken gently.
At once remove custards from water, using a wide spatula or kitchen tongs.