Combine chocolate and coffee in top of a double boiler; bring water to a boil. Reduce heat to low; cook, stirring occasionally, until chocolate melts. Gradually whisk in sugar. Add butter, 1 tablespoon at a time, whisking until melted.
Whisk eggs until thick and pale. Gradually stir about one-fourth hot mixture into eggs; add to remaining hot mixture, whisking constantly. Pour into 6 (6-ounce) greased custard cups, and place cups in a 13- x 9-inch pan. Add hot water to pan to depth of 1 inch, and cover pan with aluminum foil.
Bake at 350° for 45 minutes or until pudding appears to be set. Remove cups from pan, and cool on a wire rack. Cover and chill at least 8 hours.
Beat whipping cream at high speed with an electric mixer until foamy; gradually add powdered sugar, beating until soft peaks form. Pipe or dollop onto pudding.