Flourless Chocolate Cake

Flourless Chocolate Cake

6 tablespoons unsalted butter, plus more for pan
1 1/2 cups semisweet chocolate chips (or 8 ounces chopped bittersweet chocolate)
6 large egg yolks
6 large egg whites
1/2 cup granulated sugar
Confectioners' sugar, for dusting

Directions
Preheat oven to 275 degrees; with rack in center. Butter a 9-inch springform pan. Place butter and chocolate in a large bowl. Microwave in 30-second increments, stirring each time, until melted; cool slightly. Whisk in yolks.
In another bowl, beat egg whites to soft peaks. Gradually add sugar; beat until stiff and glossy. Whisk 1/4 of 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 center, 45 to 50 minutes. Cool completely on a wire rack. Serve dusted with confectioners' sugar.