Preheat the oven to 350 degrees F.
Place the orange juice in a small saucepan and reduce over medium-high heat to 1/4 cup. Using 1 1/2 teaspoons of the butter, lightly butter 6 (3/4-cup) ramekins. Place the ramekins in a large baking dish or roasting pan and set aside.
In a mixing bowl cream together the sugar, remaining 2 tablespoons butter, and orange zest. Add the egg yolks 1 at a time, beating well after each addition. Stir in the flour. Gradually add the orange juice; don't worry if the mixture looks curdled or appears to be separating. Stir in the milk.
In a separate bowl beat the egg whites until they just hold stiff peaks. Gently fold the egg whites into the yolk mixture in 3 additions. Do not overmix; the mixture will appear thin.
Divide the pudding cake mixture among the ramekins and add enough hot water to the baking dish to come half way up the sides of the ramekins. Cover the ramekins with a sheet of parchment paper that has been coated on one side with a non-stick baking spray. Bake until the pudding cakes are puffed and lightly firm to the touch, 30 to 35 minutes. Remove from the oven and transfer ramekins to a wire cooling rack to cool slightly.
Dust lightly with powdered sugar and garnish with a sprig of mint. Serve hot or warm.
Yield: 6 servings