Preheat the oven to 325 degrees and set a rack in the middle level. Butter an 8-inch round pan and line the bottom with a disk of parchment or waxed paper cut to fit. Butter the paper. Cut the chocolate finely and set it aside. Combine the sugar and water in a saucepan and bring to a boil over low heat, stirring occasionally to make sure all the sugar crystals dissolve. Remove the syrup from the heat and stir in the butter and chocolate; allow to stand 5 minutes. Whisk smooth. Whisk in liqueur and eggs, one at a time, into the chocolate mixture, being careful not to over mix. Place 1 inch of warm water into a small roasting pan. Pour batter into the prepared 8-inch round pan and bake about 45 minutes, until set and slightly dry on the surface. Remove round pan from the roasting pan and cool to room temperature in the pan and cover with plastic wrap. Refrigerate dessert in pan. To unmold, run a knife between the dessert and the pan and pass the bottom of the pan over the heat. Invert and remove paper. Invert to a platter. To finish, whip the cream with the sugar until it holds a soft peak. Spread the whipped cream on the top of the dessert. Decorate the top with the raspberries.