Preheat oven to 425° F. In a medium saucepan over low heat melt 2 tablespoons unsalted butter, then whisk in the zest of 1 orange, 2 cups fresh orange juice, 1/3 cup sugar, 1/4 cup corn-starch, 1/4 teaspoon salt, and 3 large egg yolks. Bring to a simmer over medium heat; cook, whisking constantly, until thickened, about 2 minutes. Pour into 4 ramekins or custard cups.
In a bowl, beat 3 egg whites and 1/2 cup sugar until the sugar dissolves and stiff, glossy peaks form. Spread the meringue over the puddings. Bake until the meringue is browned, about 10 minutes. Set the puddings in a pan of ice water to cool, then refrigerate 1 hour or until cold.