Heat oven to 400°F. Generously grease and lightly flour seven 6-oz. custard cups. In medium saucepan, melt butter and chocolate over low heat, stirring until smooth. Set aside.
In medium bowl, combine eggs and syrup; beat with electric mixer at high speed until foamy. Gradually beat in sugar; continue beating at high speed for 2 minutes until light and thickened. Add flour and chocolate mixture; beat at low speed just until blended. Fill each greased and floured custard cup about 3/4 full. Place cups on cookie sheet.
Bake at 400°F. for 11 to 15 minutes or until cakes have formed top crust, but are still soft in center. Cool 5 minutes. Invert cakes onto individual dessert plates. Sift powdered sugar over cakes. Serve warm.