- 1 7.25- to 7.41-ounce jar whole steamed chestnuts or vacuum-packed roasted chestnuts*
- 3 tablespoons unsalted butter, room temperature, divided
- 1/4 cup sugar (for coating soufflé dish) plus 14 tablespoons sugar, divided
- 2 cups whole milk, divided
- 2 tablespoons Armagnac, Cognac, or other brandy
- 1 teaspoon vanilla extract
- 1 cup egg whites (about 8 large)
- 1/8 teaspoon cream of tartar
- Bittersweet Chocolate Sauce
Blend chestnuts, 2 tablespoons water, and 1 tablespoon butter in processor until paste forms. Transfer mixture to small bowl. DO AHEAD Can be made 2 days ahead. Cover and refrigerate.
Coat inside of 14-cup soufflé dish (about 8 1/4 inches wide and 3 3/4 inches deep) with remaining 2 tablespoons butter. Sprinkle dish with 1/4 cup sugar and tilt to coat bottom and sides evenly.
Whisk 1/4 cup milk, egg yolks, 4 tablespoons sugar, cornstarch, and salt in medium bowl to blend. Bring remaining 1 3/4 cups milk and 4 tablespoons sugar to simmer in heavy large saucepan. Gradually whisk hot milk mixture into yolk mixture. Return custard to same pan. Stir over medium heat until custard thickens and boils, about 3 minutes. Remove from heat. Add chestnut paste, Armagnac, and vanilla and whisk to blend well (some small pieces of chestnut paste will remain). DO AHEAD Soufflé base can be made 2 hours ahead. Press plastic wrap onto surface; let stand at room temperature.
Position rack just below center of oven and preheat to 400°F. Beat egg whites and cream of tartar in large bowl until soft peaks form. Gradually add remaining 6 tablespoons sugar, beating until stiff but not dry. Fold whites into soufflé base in 3 additions. Transfer batter to prepared dish. Place soufflé on small baking sheet. DO AHEAD Can be made 1 hour ahead; let stand at room temperature.
Bake soufflé until puffed and just firm to touch in center, about 50 minutes. Serve immediately with sauce.
*Peeled cooked chestnuts; sold at some supermarkets and at specialty foods stores.
To serve the soufflé, use a very large spoon to gently scoop up some of the saucy interior along with a bit of the firmer sides.