Preheat the oven to 350 F. Pour the graham cracker crumbs and sugar in a small bowl and whisk together. Pour the melted butter over the top and stir with a spatula until combined. Press the mixture into a 9-inch springform pan and bake for 10 minutes, or until the crust is golden. Remove from the oven and set aside to cool (leave the oven on).
For the filling:
In the bowl of a standing mixer, beat together the cream cheese until smooth. Add the sugar and beat again until smooth. Add the sour cream, vanilla, orange zest and juice, and mix well. Add the eggs one at a time, mixing after each addition (but not too vigorously). Pour the filling over the cooled crust.
Bake the cheesecake for 50-60 minutes, until the cake has puffed significantly and the middle is still slightly jiggly (or until the cheesecake reaches 150 degrees). Move to a wire rack and let cool completely (the cake will sink a bit).
Cover the top of the cheesecake with parchment paper (just resting over the rim of the pan) and put in the fridge overnight, or for a least 8 hours.
For the glaze:
In a small saucepan, heat the heavy cream and then add the chocolate. Stir until the chocolate is completely melted. Add the vanilla and stir until the glaze is smooth. Cool to room temperature. Remove the chilled cheesecake from the springform pan and spread the glaze over the top. Let the top set before slicing.