In a large bowl, combine flour, sugar, baking powder and salt. Microwave chocolate morsels and butter in a medium microwave-safe bowl on high heat for 1 minute; stir. Microwave at additional 10-20 second intervals, stirring until smooth. Cool to room temperature. Stir in milk, eggs, and vanilla. Add chocolate mixture to flour mixture; stir (batter will be thick). Cook in a Belgian or standard waffle maker according to manufacturer's directions. Serve warm with your choice of toppings.