From Martha Stewart
6 tablespoons butter plus more for pan
1 ½ cups semisweet chocolate chips or 8 oz. chopped bittersweet chocolate
6 eggs, separated into whites/yolks
½ cup granulated sugar
confectioner’s sugar for dusting
Preheat oven to 275 degrees F with rack in center
Butter a 9 inch springform pan
Place butter and chocolate in large microwaveable bowl and microwave in 30 second intervals stiring each time until melted. Or, melt together using a double boiler.
In another bowl beat egg whites to soft peaks, gradually add sugar, beat until stiff & glossy.
Whisk ¼ whites into chocolate mixture, gently fold mixture into remaining whites
Pour into prepared pan, smooth top. Bake until cake pulls away from sides of pan and is just set in the center. 45 to 50 mintutes. Cool completely on a wire rack, serve dusted with confectioner’s sugar.