Preheat oven to 325°F. In a small saucepan, combine milk and butter, and cook over medium heat until milk is scalded and butter is melted, about 5 minutes. Remove from heat.
Place egg yolks in a bowl. Gradually whisk in hot milk. Whisk in sugar, flour, orange peel and orange juice.
In a large clean bowl, whip egg whites and salt with an electric mixer until stiff, but not dry. Fold gently into the orange mixture. Spoon pudding into 8 (6 oz.) ramekins or custard cups. Arrange cups in a baking pan or roasting pan. Add enough hot tap water to come halfway up sides of cups.
Bake puddings until tops are golden, about 15 minutes. Let ramekins cool in water bath for 10 minutes, then remove and place on a rack to cool completely. Serve pudding at room temperature or chilled.
I make this often in a lemon version. It is a family favorite -- and very inexpensive.