In a saucepan, off the heat, combine the sugar, cornstarch and zest. Whisk in the juice. Bring to a boil, stirring with a whisk.
In a bowl, beat the eggs with an electric mixer until foamy, about 2 minutes. Pour the hot orange juice mixture in a stream over the eggs, whisking constantly for about 5 minutes. Add the butter and continue whipping until the mixture is at room temperature. Spoon into four dessert dishes.
Cover with plastic wrap and refrigerate for at least 2 hours.