Preheat the oven to 325 degrees F. Set a full tea kettle of water over medium-low heat. Spray 4 (1-cup) oven-proof ramekins with nonstick cooking spray.
Separate the eggs, putting the whites in a slightly larger bowl. Using a hand mixer, whip the egg whites until they hold stiff peaks and set aside. To the yolks, add the sugar and beat until the sugar is dissolved and the color has turned a pale yellow. Add the orange zest and juice. Sift in the flour and salt and mix well. Add the milk and stir until combined.
Fold the whites into the yolk mixture. Divide the batter among the ramekins. Place the ramekins into a baking dish and pour in hot water until it reaches halfway up the sides of the ramekins. Bake the pudding cakes until set, about 20 to 22 minutes. Remove the ramekins from the water bath and let cool a bit before serving.