Remove tops from oranges, scoop out flesh, mix cornstarch with 1/4 cup orange juice. Add to remaining juice and bring to boil, stirring constantly, add rind, sugar, marmalade and butter, continuing to stir until thickened and smooth. Remove from heat, and gradually beat in egg yolks. Beat egg whites until stiff and fold into yolk mixture. Fill orange shells 2/3 full with mixture and place on baking sheet.
Bake 400F for 10-15 minutes until puffed and golden, sprinkle with icing sugar after removing from oven, serve immediately.