Sweet Potato Souffle
- 2 lb. sweet potatoes
- 1/2 cup freshly grated Parmigiano-Reggiano
- 3 Tbs. unsalted butter
- 1 white onion, minced
- 1 1/2 cups milk
- 3 Tbs. all-purpose flour
- 1/4 tsp. freshly grated nutmeg
- 1/4 tsp. ground allspice
- 1/4 tsp. ground ginger
- 6 eggs, separated
- 1 cup shredded Gruyère cheese
- Salt and freshly ground pepper, to taste
Pierce the potatoes two or three times with a fork and place on a baking sheet. Bake until easily pierced with a knife, 30 to 40 minutes. Remove from the oven and let cool. Cut in half and scrape out the pulp into a bowl. Using a potato masher, mash to form a smooth puree; you should have 2 1/2 cups. Leave the oven temperature set at 375°F.
Butter a 2-quart soufflé dish and dust the bottom and sides with 1/4 cup of the Parmigiano-Reggiano cheese.
In a large saucepan over medium heat, melt the butter. Add the onion and sauté, stirring occasionally, until soft, about 10 minutes. Meanwhile, in a small saucepan over medium heat, warm the milk until small bubbles appear along the edges of the pan; remove from the heat. Add the flour to the onion and cook, stirring constantly, for 3 minutes. (Do not brown.) Whisk in the milk all at once and simmer, continuing to whisk, until thickened, 2 to 3 minutes. Remove from the heat and stir in the nutmeg, allspice and ginger. Add the egg yolks one at a time, beating well after each addition. Add the sweet potato puree and the Gruyère cheese and stir until well blended. Season with salt and pepper.
In a bowl, using an electric mixer, beat the egg whites on high speed just until stiff peaks form. Using a rubber spatula, fold one-fourth of the egg whites into the sweet potato mixture to lighten it. Then gently fold in the remaining whites just until no white streaks remain. Pour into the prepared soufflé dish. Sprinkle with the remaining 1/4 cup Parmigiano-Reggiano cheese.
Bake until puffed and golden, 45 to 50 minutes. Serve immediately.