Turn the base of an 8-inch springform pan upside down to make it easier to remove the cheesecake later. Line the bottom with parchment paper and secure the sides. Lightly grease the sides of the pan with butter. Set aside.
PREPARE THE CRUST:
Place the chocolate wafer cookies into the bowl of a food processor. Pulse until cookies turn into a fine crumb. Add the butter and sugar and pulse again until combined. Spread the cookie mixture in the bottom of the prepared pan. Press down firmly (especially at the outside edges of the pan, and refrigerate for 1 hour.
PREPARE THE CHEESECAKE:
While the crust is chilling, place the chocolate in a heat-proof bowl set over a pan of hot (not boiling) water. Heat until melted, stir occasionally. Remove the bowl of melted chocolate from the saucepan and set aside to cool.
In a medium mixing bowl, beat the whipping cream with an electric mixer until soft peaks form. Set aside.
In a clean large mixing bowl, using the same mixer, combine the granulated sugar and cream cheese. Beat well until combined. Add the cooled chocolate and mix on low until blended. Add the whipped cream mixture into the chocolate cream cheese mixture and blend on low. Add the Irish cream and vanilla and blend on low until incorporated. Scrape down the sides of the bowl and blend another few seconds. Spoon the cheesecake mixture into the cake pan and smooth the top, an off-set spatula works best here. Lightly cover top with plastic wrap and chill until firm, at least 2 hours or overnight.
Remove the sides of the pan and gently transfer to a serving plate. Cut into slices using a warm, dry knife. Serve immediately garnished with sweetened whipped cream, strawberries and chocolate shavings, if desired.