How to Make It
In a small, heavy saucepan, whisk the egg yolks with the eggs, orange juice, sugar and cornstarch. Cook over moderate heat, whisking constantly, until the mixture thickens and reaches 180° on a candy thermometer, about 5 minutes. Strain the custard through a fine sieve set over a bowl. Let cool to room temperature, stirring a few times. Press a sheet of plastic wrap directly on the custard and refrigerate until very cold, about 1 hour.
Meanwhile, using a sharp knife, peel the oranges, removing all of the bitter white pith. Cut in between the membranes to release the sections. Cut the orange sections into 1/2-inch dice.
Spoon the oranges into glasses or bowls and top each serving with 1 teaspoon of the orange liqueur, 1/4 cup of the orange custard and a scoop of the ice cream. Serve.