Preheat oven to 375 degrees F. Butter 8 to 10 (4-ounce) souffle dishes with a pastry brush and dust lightly with sugar. Bring 3/4 cup milk to a boil in a medium saucepan. Meanwhile, whisk 3 tablespoons sugar, flour, cornstarch, and 1/4 cup milk in a medium bowl to combine. Slowly whisk in the hot milk, and return mixture to the saucepan. Bring to a boil and cook for 1 to 2 minutes. Remove from heat and add the egg yolks, 1 at a time, whisking thoroughly after each addition. Add the chestnut puree, brandy, and vanilla and 1 tablespoon butter; stir well to combine. In a large bowl, whisk the egg whites until they form soft peaks. Add a pinch of salt and remaining 2 tablespoons sugar; continue whisking until stiff peaks form. Whisk 1/3 of the whites into the chestnut mixture, then fold in remaining whites. Divide mixture between souffle dishes. Run your thumb along the inside edge of each dish to remove any spilled batter. Transfer to oven and bake for 10 to 12 minutes (8 minutes if using a convection oven). Remove from oven. Just before serving, poke a hole in the top of each souffle and pour in 2 tablespoons Brandy Custard Sauce. Serve immediately.
In a heavy-bottomed medium saucepan, scald milk, cream, 6 tablespoons sugar, and vanilla bean over medium heat. Meanwhile, whisk together 6 tablespoons of sugar and egg yolks. Temper egg yolks by adding about 1/3 of the milk mixture to the yolks, whisking constantly. Combine the egg mixture with remaining milk in saucepan and continue whisking until thickened over low heat. The custard sauce is done when it coats the back of a spoon. Cool to room temperature, and add brandy. Yield: about 3 cups