Preheat oven to 350 F. Bring 4 cups of water to a boil.
While water heats, in a large bowl, whisk together 2/3 of the lemon zest, lemon juice, orange juice, ginger root and egg yolks. Slowly whisk in milk and vanilla extract. Add 1/2 cup sugar, salt and flour. Whisk until smooth, and set aside.
With a hand mixer, whip the egg whites until they hold soft peaks. Whisk a quarter of the whites into the yolk mixture. Gently fold in the remaining egg whites, being careful not to overmix or deflate them.
Place 4 mini cocottes into a deep baking dish or roasting pan. Divide batter among the cocottes. Set the baking dish into the oven and carefully pour boiling water into the dish until it reaches at least halfway up the sides of the cocottes.
Bake 30 minutes, or until the cakes are browned and puffed. Remove the cocottes to a cooling rack and let cool for 10 minutes. Dust with the remaining lemon zest and sugar.