Prepare cupcake pans with liners. Place the Oreo cookies in a food processor and pulse into a crumble. Melt the butter and stir into the cookie crumbles. Place about a teaspoon of cookie mixture into the bottom of each cupcake liner and press into the bottom using a spoon or something that fits (like a shot glass or the top of a bottle). Place the pan in the freezer while you prepare the filling.
Put the cream cheese and powdered sugar in a large mixing bowl, and beat with a hand mixer until smooth (you can also use your stand mixer). Add in the Irish cream and mix in.
Melt the white and semi-sweet chocolate chips in a microwave-safe bowl or container with a spout (my glass mixing cup worked perfectly). Cook for one minute, remove and stir and cook again for another 30 seconds. If the chocolate is not completely melted, zap again in the microwave for an additional 20 seconds.
Pour the melted chocolate in a steady stream into the cream cheese mixture while the mixer is running at low speed, scraping the sides of the bowl as needed. The chocolate will start to harden pretty quickly. You may end up with a few small chocolate pieces in the batter, but don't worry, everything will still mix together fine.
Fold in ½ cup of the whipped cream (or whipped topping) with a spatula (see notes for how to make homemade whipped cream). Remove the pans(s) from the freezer and spoon or pipe the filling into each liner. I found that a simple piping bag with no tip worked great. Place the pan(s) back into the freezer for 3 hours to firm and set.
Once the cheesecakes are ready, remove the pan(s) from the freezer. If desired, carefully remove each cheesecake from the liner (this is optional but makes a pretty presentation). Pipe or spoon a dollop of whipped cream on top of each mini cheesecake and sprinkle with chocolate shaving (see notes) and/or sprinkles. Place the cheesecakes in the refrigerator for 30 minutes or until ready to serve. Enjoy!