First, a little prep work. Put chocolate bar, bowl and beaters for the cream in the freezer. Dissolve instant coffee with a couple of tablespoons of cream. Set aside.
Beat softened cream cheese with ¼ cup heavy cream and sour cream until completely smooth. Add dissolved coffee, melted chocolate chips and vanilla, beat until well combined. Set aside. Add cold cream to cold bowl and beat cream until it thickens and peaks form. Add sugar (or sugar substitute for baking that measures equally, like Splenda) and mix until combined. Add cheese mixture to cream and mix until well combined.
To assemble the cake, cover the bottom of an 8 inch springform pan with chocolate chips cookies, breaking a few to cover as well as you can. Spread 1/3 of the mocha filling over the cookies evenly. Continue layering cookies, lying flat and touching sides, followed by mocha filling twice more. Smooth the top, cover with plastic wrap and refrigerate 6 hours to overnight (recommended).
Before serving, use a vegetable peeler make chocolate shavings from the frozen candy bar for garnish. Run a small sharp knife around the edge to remove the sides of the springform pan.