- 12 ounces bittersweet chocolate, chopped
- 1 stick unsalted butter, cut into tablespoon pieces, plus more for greasing
- 1 vanilla bean, cut lengthwise
- 1/4 teaspoon salt, plus a pinch for the egg whites
- 12 tablespoons sugar
- 5 large eggs, separated into yolks and whites, at room temperature for 30 minutes
- 1/4 cup all-purpose flour
Put an oven rack in the middle position and preheat the oven to 350 degrees F. Butter a 6-cup souffle dish or casserole.
Melt the chocolate and butter in a large bowl set over a pan of barely simmering water, stirring frequently. (Or in a microwave-safe glass bowl in a microwave at 50 percent power for 2 to 3 minutes, stirring well every 30 seconds until the chocolate is melted and smooth.) Cool completely.
Scrape the seeds from the vanilla bean into the cooled mixture and add salt and 6 tablespoons sugar. Add yolks 1 at a time, whisking well after each addition. Whisk in the flour.
Beat the whites with a pinch of salt in a bowl using an electric mixer at high speed until they hold soft peaks. Add the remaining 6 tablespoons sugar, a little at a time, beating until the whites hold stiff glossy peaks.
Bake about 30 to 35 minutes or until the center is still jiggling and a toothpick inserted in the center comes out with moist crumbs adhering to it. Serve the souffle warm.