Prepare pie dough using the linked recipe.
Cook's Tip: The pie is baked on the lowest rack of the oven to make sure the bottom is crisp rather than soggy. Beginning with a hot crust and hot pumpkin filling also allows less time for the pumpkin mixture to seep into the crust before it starts to cook and set. Prepare for ooo-ing and ah-ing as guests take their first bite.
As soon as the crust goes into the oven, gather the first 6 ingredients for the pumpkin custard: pumpkin, brown sugar, cinnamon, ginger, nutmeg and salt, and place into a food processor.
Blend until well combined and transfer to a quart-size pot. Place over medium heat until pumpkin mixture begins to sputter and then cook for an additional 5 minutes, stirring frequently until pumpkin mixture looks smooth and shiny. Turn off heat.
While the pumpkin mixture heats, place eggs in the food processor and process them until well-combined.
Into the pumpkin mixture, whisk in sour cream, heavy cream and milk, one at a time, stirring after each addition until fully combined. Heat mixture back to a sputter, stirring constantly. Turn heat off.
With the food processor running, slowly pour in half the hot pumpkin mixture. Stop the processor. Scrape the rest of the pumpkin in mixture into the food processor with a spatula and process for 30 seconds.
When the crust comes out of the oven, evenly sprinkle chocolate chips over crust. Within several minutes, they all should have melted into a single layer. Keep oven on, lowering temperature to 375°.
Gently ladle the hot pumpkin mixture over chocolate layer. If poured quickly, the pumpkin mixture will push the chocolate layer out to the sides of the pie.
Bake at 375° for 40–50 minutes on the very bottom rack of oven until filling puffs up, cracks lightly around the edges and center is like Jell-O, rather than liquid. Let cool on a wire rack for at least an hour.
For the optional topping, melt 1/2 cup chocolate chips in a double boiler. (If you don't have one, fill a larger pan with several inches of water and place a smaller pan inside).
Add a teaspoon of neutral oil like grapeseed to make sure chocolate stays shiny when cooled.
Using a spoon, drizzle the melted chocolate over the pie.
Top with candied or toasted hazelnuts.