Prep. Preheat the oven to 350°F and liberally grease an 8-inch round baking dish with butter.
Boil. Add the carrots to a pot and cover with water. Boil for 20 to 25 minutes or until the carrots are tender. Drain the carrots.
Cool. Allow the carrots to cool to room temperature.
Puree. Add the cooled carrots to a food processor or blender and puree until smooth. Pulse in the sugar, butter, eggs, and vanilla, followed by the flour, baking powder, cinnamon, nutmeg, and salt. Pulse until everything is nice and smooth. Transfer the mixture to a large mixing bowl and set aside.
Whip the egg whites. Beat the egg whites with an electric mixer at high speed until stiff peaks form.
Put it all together. Using a rubber spatula, gently fold the egg whites into the carrot mixture.
Bake. Pour the souffle batter into the greased baking dish and bake for 45 to 50 minutes or until the souffle is puffed up and the top is golden brown.
Remove from the oven and let it stand for 5 to 10 minutes before serving.
Notes
Cooled Carrots: Cool the boiled carrots to room temperature before mixing.
Room Temp Egg Whites: Use room-temperature egg whites for better volume and a fluffier soufflé.
Fold Gently: Carefully fold the egg whites into the carrot mix to keep the airiness intact.
Storage Tips: Transfer the soufflé to an airtight container and refrigerate for up to 4 days or freeze for 3 months.
Reheating: Thaw if frozen, then reheat covered with foil in a 350°F oven for 10 to 15 minutes or microwave in 30-second intervals until warm.