Step 1

Preheat oven to 325 degrees F. Line an 8-inch square baking dish with parchment paper.

Step 2

In a medium bowl, beat egg whites until stiff; set aside. In a large bowl, beat egg yolks, granulated sugar, butter, and vanilla until creamy. Gradually add flour and cocoa and beat until thoroughly mixed. Add milk and mix well. Gently fold in egg whites until thoroughly blended. Pour batter into baking dish.

Step 3

Bake 55 to 60 minutes, or until toothpick inserted in center comes out dry. Let cool, then refrigerate at least 6 hours. Sprinkle with confectioners' sugar before serving.