To Make Crust:
Preheat oven to 325 degrees F. Assemble a 9-inch springform pan with the raised side of the bottom facing down.
Place gingersnaps in food processor and process until fine crumbs form. Move ginger crumbs to small bowl and add melted butter. Press mixture into bottom of springform pan. Place pan on a rimmed baking sheet; bake 10 minutes, and set aside.
To Make Filling:
In a large bowl, mix sugar, flour, nutmeg, salt, and cream cheese. Add vanilla and mix 1 minute. Add eggs to cream cheese mixture, one at a time.
Add cream, milk, Kahlua, and melted chocolate; blend until smooth, scraping down sides of bowl as needed.
Pour filling onto crust, and bake just until set, 1 hour. Turn oven off, and let cheesecake sit 1 hour in oven, without opening (this helps prevent cracking).
Run a thin knife around the edge of the pan (this helps prevent cracking, too); leave in pan, and cool completely on wire rack. Cover loosely and refrigerate, at least 6 hours, preferably overnight so the flavors have time to blend and the texture becomes nice and firm.
Unmold cheesecake. As an option drizzle some Mexican Chocolate Sauce over each slice.
To make Chocolate Sauce:
Heat 1/2 cup cream in a heavy saucepan over medium heat until cream comes to a low boil.
Remove the pan from the heat and add Mexican chocolate. Let chocolate sit in the hot cream 3 to 5 minutes to soften, and then whisk chocolate together with the cream. Stir in butter, cocoa powder (optional), vanilla, cinnamon, and liqueur (optional).
If chocolate becomes too thick, stir in more cream, 1 tablespoon at a time, to desired consistency.