Preheat oven to 325°F. Place an 8 x 8 pan on bottom rack and fill halfway with boiling water.
Spray a 9 inch springform pan with cooking spray. Wrap bottom of pan with aluminum foil. Set aside.
In a medium-size mixing bowl toss together graham cracker crumbs with sugar and butter until fully moistened. Press onto bottom and halfway up sides of pan. Place pan into freezer while you make filing.
Using an electric mixer, whip together cream cheese, sugar and vanilla until completely smooth. Add eggs one at a time mixing well after each addition. Scrape sides and bottom of bowl as needed.
Add cocoa, cornstarch and food coloring, mixing well. Lastly, on low speed add sour cream and buttermilk. Beat on low just until combined. Avoid beating too much air into the filling.
Pour evenly into crust. Bake on middle rack of oven for 1 hr 30 - 1 hr 40 minutes or until the center is still slightly loose when gently shaken. It won't be completely set. Turn off oven, leave door slightly ajar, and leave cheesecake in oven for 1 hour longer to gently finish baking.
Remove to a cooling rack, and allow to cool for 30 minutes then run a knife gently around top edge. Cool completely to room temperature. Leave ring in place, wrap and chill for at least 12 preferably, 24 hours.
To make the topping: In a medium-size mixing bowl use an electric mixer to cream together cream cheese, butter, cream and vanilla. Beat until fully combined, lower the speed of the mixer and gradually add powdered sugar. Whip until fluffy.
Spread evenly on chilled cheesecake and decorate as desired. Garnish the top with grated white chocolate. Return to fridge for 1-2 hours to set.
Store leftovers chilled.