Butter a 9' springform pan.
Put cookies into food processor and grind into a crumb.
Pour crumbs into a bowl.
Pour melted butter over crumbs, mix to combine.
Press firmly on bottom of springform pan to form a crust. Cover with plastic wrap.
Place chocolate in a bowl.
Heat 1 cup heavy cream, espresso powder to just a boil.
Pour over chocolate, let sit 2 minutes.
Add in the Kahlua and vanilla, mix in small circles to mix completely until ganache forms.
Let cool at room temp for 60 minutes or covered in the refrigerator for 30 minutes.
In bowl of mixer with whisk attachment, whisk 1 3/4 cups heavy cream into stiff peaks.
Whisk the ganache to fluff it up.
Fold in the whipped cream into the ganache to form the mousse.
Scoop over chilled crust, spread evenly with spatula. Refrigerate minimum 6 hours (I chilled mine over night).
When ready to serve make whipped cream. Whisk remaining 1 3/4 cups heavy cream and powdered sugar into medium peaks. Spread over tart.
Sprinkle with chocolate shavings. I took a vegetable peeler and peeled the edge of a chocolate bar to get my shavings.