In a medium saucepan combine butter and unsweetened chocolate. Cook and stir over medium-low heat just until melted and smooth. Remove from heat. Stir in sugar. Add eggs and vanilla, stirring until combined. Stir in flour, baking powder, and salt. Whisk in milk until smooth.
Add batter to a preheated, lightly greased regular or Belgian waffle baker according to manufacturer's directions. Close lid quickly; do not open until done. Bake according to manufacturer's directions. When done, use a fork to lift waffle off grid. Repeat with remaining batter.
Meanwhile, for mocha syrup, in a small saucepan combine semisweet chocolate pieces, whipping cream, and coffee liqueur. Cook and stir until chocolate is melted and mixture is smooth.
Serve waffles warm with ice cream and mocha syrup.