Whisk together in a bowl, the egg yolks, the flour, 1/2 cup sugar, orange zest and the orange juice. Place this mixture in a saucepan and heat gently to a boil, stirring continuously with a wooden spoon. Cook until the cream coats the back of the spoon. Cool and stir several times to prevent a skin from forming on top. Beat 3 egg whites until firm with the rest of the sugar. Fold them gently but thoroughly into the cold mixture with a spatula. Pour into a glass bowl and refrigerate.
