Grease and flour a 9-inch springform pan.
Melt the semisweet chocolate, unsweetened chocolate, and butter with the water in a medium saucepan over low heat, stirring with a wire whisk until smooth. Cool slightly.
In a large mixing bowl, beat eggs, sugar, and vanilla on high speed for 10 minutes. Fold in chocolate and liqueur.
Transfer batter to the prepared pan. Place pan in a shallow baking pan. Bake in a 325 degree F oven for 35 to 40 minutes or until cake is slightly puffed on outer one-third of top and center doesn't shake when you move the springform pan gently. (Cake should feel firm all over, except in center.)
Remove springform pan to a wire rack to cool for 20 minutes. Loosen and release the sides of springform pan, but leave the cake in the pan until completely cool. Remove the cake from pan. Cover and chill for 6 to 48 hours.
Serve with whipped cream. Store in refrigerator. Makes 16 servings.
This fudgy cake will dip in the center after it's baked. Disguise this by filling the center with whipped cream and fruit, if you like.