4 ounces semisweet chocolate bits
1 stick (1/2 cup) unsalted butter
3/4 cup sugar
3 large eggs
1/2 cup unsweetened cocoa powder plus additional for sprinkling
Preheat oven to 375°F. Butter an 8-inch round pan and dust with sugar.
In a double boiler of barely simmering water melt chocolate with butter, stirring, until smooth. Remove top of double boiler from heat and whisk sugar into chocolate mixture. Add eggs and whisk well. Sift 1/2 cup cocoa powder over chocolate mixture and whisk until just combined. Pour batter into pan and bake 25 minutes, or until top has formed a thin crust. Cool cake and invert onto a serving plate. Sprinkle with confectioner's sugar right before serving.