6 tbls unsalted butter plus more for pan
1 1/2 cups semisweet choclate chips or 8 ounces chopped bittersweet choclate
6 large egg yolks
6 large egg whites
1/2 cup granulated sugar
1. Preheat oven to 275′, with rack in center. Butter a 9-inch springform pan. Place butter and chocolate in large bowl. Microwave in 30-second increments, stirring each time, until melted; cool slightly. Whisk in yolks.
2. In another bowl, beat egg whites to soft peaks. Gradually add granulated sugar; beat until stiff and glossy. Whisk 1/4 of whites in to chocolate mixture; gently fold mixture into remaining whites.
3. Pour into prepared pan; smooth top. Bake until cake pulls away from sides of pan and is just set in center, 45 to 50 minutes. Cool completely on a wire rack. Serve dusted with confectioners’ sugar.