Makes 6 soufflés
6 medium oranges (about 2 1/2 inches wide)
3 large eggs, separated
1/3 cup sugar PLUS 2 Tbsp sugar, and more for sprinkling
3 Tbsp cornstarch
1 cup freshly squeezed orange juice
1/4 cup milk [not skim]
2 tsp freshly grated orange zest
1 Tbsp Grand Marnier liqueur OR defrosted orange juice concentrate
Pinch of salt
Powdered sugar, to serve
Cut off the top part of each orange (about 3/4-inch) and a tiny sliver from the bottom so the oranges can stand straight. Using a microplane grater, grate the zest from the top part. Reserve 2 teaspoons for this recipe, then freeze the rest for another use. Empty the orange shells with a grapefruit spoon (making sure not to pierce the skin). Press the orange flesh through a strainer. Measure out 1 cup of juice for this recipe. Set orange shells on a large baking tray.
Preheat the oven to 375 degrees F. Dry orange shells if damp and lightly grease the insides with softened butter. Sprinkle bottoms and sides with excess sugar. Shake out extra.
Separate the eggs. In a medium bowl, whisk the egg yolks with the sugar and cornstarch until smooth. Whisk in the orange juice and milk. Place the mixture in a saucepan and heat over medium heat while stirring constantly until it thickens. Remove from the heat and add the zest, Grand Marnier, and salt. Let cool completely.
Using an electric mixer, whisk the egg whites until they hold soft peaks, then gradually add the 2 tablespoons of sugar and keep whisking just to stiff peaks. Fold 1/4 of egg whites into the orange custard to lighten, then add the custard mixture to the egg whites and gently fold in until fully incorporated. Fill the orange skins just to the top with the mixture. Flatten the tops with a spatula. Use your finger or a damp cloth to wipe clean the rim of the orange skins. Bake for about 20 to 25 minutes, or until puffy and golden on top. Sprinkle with powdered sugar and serve immediately.