Preheat oven to 375°F.
Butter a 1 1/2-quart soufflé dish, or four individual ramekins, and sprinkle with 1 tablespoon of the sugar.
Beat the egg yolks until thick and yellow. Add the zest of 1 Cara Cara orange and 1/4 cup sugar.
Measure the flour into a saucepan, and then add the milk slowly, whisking as you do until thoroughly blended.
Blend in the egg yolk mixture, stirring as you do.
Continue to stir over a medium setting until the mixture comes to a boil and thickens.
Stir in the orange juice, and remove from heat.
In a bowl, add the egg whites and cream of tartar, along with a dash of salt. Beat with whisk or mixer until soft peaks form.
Continue to beat as you add 2 tablespoons sugar. The whites should be stiff.
Fold the egg white mixture into the custard gradually, a quarter or a third at a time.
Transfer to the prepared soufflé dish.
Bake for 40 minutes. The soufflé should be puffy and set.