Prepare the Crust — Preheat oven to 350°F (175°C). Lightly grease and line a 9x9-inch pan with parchment paper, leaving an overhang for easy removal. In a food processor, combine flour, sugar, and salt. Add cold, cubed butter and vanilla, then pulse until the mixture comes together into a dough. Press the dough evenly and firmly into the prepared pan. Bake for 20–25 minutes, until the edges are lightly golden. Let sit at room temperature for 20 minutes to cool before pouring the pumpkin filling.
Make the Pumpkin Filling — In a large bowl, whisk together pumpkin, brown sugar, eggs, heavy cream, vanilla, cornstarch, cinnamon, ginger, nutmeg, salt, and pepper until smooth. Place in the fridge until ready to pour over the shortbread crust. Re-whisk the mixture right before pouring to ensure a smooth filling, then pour over the par-baked crust.
Bake the Bars — Pour the filling over the warm but not hot crust. Return the pan to the oven and bake for 50–55 minutes, or until the filling is set and the center jiggles just slightly when you shake the baking dish.
Cool & Chill — Cool completely at room temperature, then refrigerate for at least 6 hours (overnight is best) for clean slicing.
Slice & Serve — Lift the bars from the pan using the parchment overhang. Slice into squares and top with whipped cream and a sprinkle of cinnamon.