Preheat oven to 450 degrees. In a large bowl combine together graham cracker crumbs, sugar and butter. Press into 9 inch springform pan, pushing crumbs up sides. Put pan into freezer and chill.

Melt chocolate and butter together in microwave for about 1 minute. In a large bowl using a hand mixer, beat together cream cheese, sugar and vanilla until light and fluffy. Add in eggs one at a time until well combined. Mix in cream. Remove 2-3 cups of mixture to a smaller bowl and stir in melted chocolate. Pour remaining batter into chilled crust. Drizzle in chocolate batter and swirl with knife. Bake for 15 minutes then reduce oven temperature to 300 degrees and bake for another hour. Turn off oven and let cheesecake cool in oven for 30 minutes and then cool to room temperature