Prepare the filling-

Toast the pumpkin: In a small heavy-bottomed saucepan, heat the pumpkin puree over medium heat, stirring constantly, until fragrant, about 3-5 minutes. 

Transfer toasted pumpkin puree to a medium mixing bowl and whisk in dark brown sugar and cream, followed by egg and vanilla (be sure to add the cream before the egg so the warm pumpkin doesn't scramble the egg). Whisk to combine. Add cornstarch, whisking until very smooth, followed by cinnamon, allspice, ginger, salt, cloves, nutmeg, and black pepper. Cover and refrigerate 1 hour, up to overnight, to allow flavors to meld. 

Make the crust-

Preheat oven to 350 degrees F. 

In a large zippered storage bag, crush the graham crackers and pecans together using a rolling pin or by hand until very fine crumbs form.

Transfer crumbs to mixing bowl. Add dark brown sugar, melted butter, and salt, mixing until all crumbs have absorbed butter evenly. 

Line an 8x8-inch baking pan with parchment paper. Transfer crust mixture to the prepared pan. Spread the crumbs evenly in the bottom of the pan, using fingers to press firmly to create an even, firm crust.

Bake crust for 8 minutes until just golden. Remove from oven. Leave oven on. 

Add filling to pre-baked crust (no need to let the crust cool), spreading evenly and smoothing the surface with a spatula.

Bake filled crust for 30-35 minutes until center does not jiggle when gently shaking pan. 

Let cool to room temperature before refrigerating for at least 1 hour before serving. This allows for easier slicing, but also the best texture.

Serve with whipped cream if desired.