Move the oven rack to the middle position and preheat the oven to 325 degrees Spray a 13x9-inch pan with nonstick cooking spray.
In a medium bowl mix together the graham cracker crumbs, sugar, and melted butter until mixture resembles web sand. Then, press the crust mixture into the bottom of the prepared pan.
In a large mixing bowl, use a hand mixer on medium speed to beat together the cream cheese and sugar. Turn the mixer off, add the eggs, and beat on low speed until incorporated. Turn the mixer off, add the pumpkin, pumpkin spice, vanilla, and salt, and beat on low speed until combined.
MAKE & BAKE CHOCOLATE LAYER
Remove 1 ¼ cups of the cheesecake mixture from the bowl and set aside.
In a small saucepan over low heat add the chocolate and butter and stir frequently until chocolate is melted. Pour chocolate mixture into 1 ¼ cups pumpkin mixture and whisk until combined.
Pour mixture over crust, spread into an even layer, and bake for 15 minutes.
BAKE CHEESECAKE LAYER:
Pour remaining cheesecake mixture over chocolate layer and spread into an even layer. Bake for 40-45 minutes, or until set. Move to a wire rack to cool completely, about 2 hours.
MAKE WHIPPED CREAM:
In a medium bowl add whipping cream and sugar and beat with an electric mixer until stiff, about 3-4 minutes.
Spread whipped cream in an over layer over completely cool cheesecake bars. Cover pan and chill for at least 3 hours or overnight.
Sprinkle with nutmeg, slice into 24 bars and serve.