Generously butter a 9-inch springform pan. Break the chocolate wafers into a food processor fitted with the steel blade. Pulse until you have fine crumbs.
Add the melted butter; pulsing just to blend.
Empty contents in the pan press the crumbs onto the sides with the back of a spoon, making a 1 1/2 -2-inch border. Use a flat-bottomed glass to press the remaining crumbs on the bottom of the pan, being sure to press firmly into the sides. Refrigerate while you prepare the filling.
Position rack in the lower third of the oven and preheat to 325 degrees.
To make the filling:
Place chocolate chips and water in a small heat-proof bowl. Set the bowl in a pan of simmering water and stir until melted, or melt in a microwave on medium setting. Blend in the liqueur, Spoon the chocolate over the cooled crust, spreading it evenly with the back of a spoon. Set aside.
Put the cream cheese in the large bowl of an electric mixer fitted with the beaters or paddle attachment. Mix for 30 to 45 seconds on medium speed, until smooth and creamy.
Add the sugar in a steady stream, taking about 30 to 40 seconds. Scrape the sides of the bowl as necessary. Mix 1 minute longer or until very smooth.
Reduce the mixer speed to medium-low. Add the eggs, one at a time at 30 - second intervals, mixing well after each addition. Add the vanilla and sour cream and blend for 30 seconds longer, scraping the sides of the bowl again as necessary.
Pour the cheese filling over the chocolate starting around the sides, then filling in the middle. Smooth surface with the back a spoon. Be careful not to disturb the crumb crust. Bake in preheated oven for 50 minutes.
Turn off the heat and without opening the oven door, leave the cake in the oven for an additional hour. Remove from oven. Set on a cake rack to cool 3 hours or longer. Refrigerate at least 24 hours before serving.
To Serve:
ABout 1 hour before you are ready to serve, run a thin knife around the edge of the pan and carefully remove the rim. Transfer the cheesecake to a cake platter and garnish as follows:
Imagine that the surface of the cake is the face of a clock. starting at 12 o'clock, press the long side of the candy gently against the cake. Push down on the left side of the mint, pushing into the cake at an angle.
Only top of the mint, which will form an elongated triangle, will be showing Continue with three more mints, inserting them at 3, 6, and 9 o'clock. Then insert the remaining mints evenly around the top of the cake. Leave the cake at room temperature until ready to serve.
Storage: Refrigerate, covered with aluminum foil, for up to one week.