Preheat oven to 425°F (220°C). Grease bottom of a 9-inch square baking pan.
Melt butter over low heat. Add cocoa and 1 cup sugar; stir well. Remove from heat; cool about 5 minutes. Stir in flour and vanilla. Add egg yolks, one at a time, beating well after each addition.
Beat egg whites with 1 tablespoon sugar until soft peaks form; gradually fold into chocolate mixture. Spoon batter into prepared pan.
Bake in preheated oven 18 to 20 minutes or until edges are firm (center will be slightly soft). Cool completely. Refrigerate for about 4 hours. Let stand at room temperature about 15 minutes before serving. Garnish with confectioners' sugar.
Makes 20 servings.
Recipe adapted from Hersheys.
Date: April 3, 2004