Preheat oven to 350°F Grease a 9 inch springform pan, or use a 9 inch square pan, preferably lined with parchment paper.
To make the brownie layer:.
In a large mixing bowl mix together pumpkin, sugar, oil and vanilla. Sift in the flour, cocoa powder, cornstarch, xanthan gum, baking soda and salt and stir to combine, then mix in the melted chocolate.
To make the pumpkin layer:.
Mix all ingredients in a large mixing bowl and beat until thoroughly combined.
Use a spatula to spread the brownie layer into the prepared baking pan, taking care to bring the batter to the edges of the pan. Pour the pumpkin layer over it, leaving a little room at the edges if you can. Bake for 30 minutes, until the pumpkin layer looks fairly firm (a little jiggling is okay) and has cracked at the edges a bit.
Let cool for 20 minutes and then transfer to the fridge to set for at least an hour and a half. Once set, decorate with chocolate chips and serve.