Preheat the oven to 325°F with the rack in the middle position. Place six individual 6-ounce molds in a baking dish or roasting pan big enough to hold them comfortably.
In a medium saucepan, whisk together milks and half-and-half; add cinnamon stick and lemon zest. Bring to boil over medium-high heat, remove from heat. Cover and let stand 15 minutes. Discard cinnamon stick and zest.
Meanwhile, in a small saucepan over medium-high heat, combine 3/4 cup of the sugar and 1/3-cup water and bring to a boil. Cook until mixture turns deep amber color, swirling pan off burner as color deepens to prevent burning. Quickly pour caramel into molds.
Heat kettle of water to a simmer.
In a large bowl, thoroughly whisk whole eggs, egg yolks, vanilla, and remaining 1/4 cup sugar. Slowly whisk in warm milk mixture. Strain liquid through fine-mesh strainer into a pitcher, then pour into molds.
Place baking dish on pulled-out oven rack. Fill dish with simmering water so it reaches halfway up Side Dish of molds. Bake for 45 to 50 minutes, until custards are just set in middle. Let cool to room temperature, then transfer to refrigerator to chill at least 4 hours.
To serve, run knife around edges and invert onto plate.