Preheat the oven to 325 degrees and grease a 9 inch springform pan.
Mix the ingredients for the crust, very well, until all evenly incorporated. (Not the chocolate pieces.) Press graham cracker mixture into the pan, evenly, all over the bottom and about half way up the side.
Break up the chocolate bar and lay the chocolate pieces all over the crust, evenly.
Start beating the cream cheese in a mixer, on medium-high speed, for about 2 minutes.
Add the vanilla extract, sour cream, and pumpkin puree. Beat until completely combines. Scrape sides and bottom of the bowl.
Add the eggs, one at the time, beating after each addition. Scrape sides and bottom of the bowl.
Add sugar, spice and corn starch. Mix on low speed. Make sure that all ingredients are well combined.
Pour the cheesecake batter into the pan with crust. Sprinkle chopped pecans over the top.
Bake for 55-60 minutes.
Take it out of the oven and let it rest for 10 minutes on the counter and then gently run a greased butter knife between sides of the cheesecakes and the springform to carefully separate it. (You don't actually have to take the cheesecake out of the pan until ready to frost.)
Cool cheesecake for an hour and then place it in the refrigerator. Refrigerate for at least 4 hours before servings.
Drizzle chocolate syrup of hot fudge topping over the cheesecake when ready to serve. (If you put it on hot cheesecake, most of it will run off fast.)