2 Tbsp. plus 1 tsp. unsalted butter, divided
¼ cup plus 2 Tbsp. grated Parmesan, divided
1 medium zucchini (about ½ lb.), peeled
1 cup whole milk
¼ cup flour
1 Tbsp. finely chopped fresh basil
2 tsp. ground mustard
1 tsp. garlic powder
1 tsp. onion powder
½ tsp. kosher salt
¼ tsp. freshly ground black pepper
4 egg yolks
5 egg whites (preferably unpasteurized)
½ cup grated Gruyere
• Preheat the oven to 400 degrees. Grease a 2-quart soufflé dish with 1 teaspoon butter. Dust the inside of the dish with 2 tablespoons Parmesan and shake out the excess. Set aside.
• Trim the stem and root from the zucchini and discard. Using a food processor or box grater, grate the zucchini and roll it in a clean kitchen towel, pressing out as much moisture as possible, then set aside.
• In a small pot, warm the milk over medium-low heat, stirring occasionally.
• In a large saucepan, make a roux by melting the remaining 2 tablespoons butter over medium heat. Whisk in the flour, stirring constantly until the flour loses its raw smell, 2 to 3 minutes.
• Remove the roux from heat and stir in the warm milk, basil, mustard, garlic powder, onion powder, salt and pepper. Return to medium heat, whisking constantly until it thickens and no lumps remain, about 3 minutes.
• Remove the mixture from heat and add the egg yolks one at a time, whisking until incorporated. Stir in the remaining ¼ cup Parmesan, the Gruyere and the zucchini. Set aside.
• Using a hand mixer on high speed, whip the egg whites until stiff, shiny peaks form, about 5 minutes. Gently fold the egg whites into the zucchini mixture, ¼ cup at a time.
• Lightly spoon the soufflé mixture into the prepared dish. Place the soufflé in the oven and reduce the heat to 375 degrees. Bake 30 to 40 minutes, until the soufflé rises and the top is browned. Serve hot.