Make the crust:
20 chocolate wafer cookies
2 T sugar
3 T unsalted butter, melted, plus more for pan
4oz semisweet chocolate, melted
Preheat oven to 350. In a food processor, pulse cookies and sugar until finely ground. Add butter and pulse until crumbs are moistened. Press crumbs into the bottom (but not sides) of a 9" removable-bottom tart pan. Place tart pan on a rimmed baking sheet; bake until set, about 12 minutes.
Pour chocolate onto warm crust. Spread with a spatula. Freeze until chocolate is firm, about 5 minutes. Brush sides of tart pan with butter. Set aside.
Make the filling:
1 1/2 C canned pure pumpkin puree
1/2 C heavy cream
1/4 C packed light brown sugar
1/4 C pure maple syrup
1/2 tsp pumpkin pie spice
1/4 tsp salt
In a bowl, whisk together pumpkin, egg, cream, sugar, maple syrup, pumpkin pie spice, and salt. Pour filling into prepared crust; bake on a rimmed baking sheet until set, about 45-50 minutes. Cool 1 hour at room temperature; refrigerate 1 hour. Remove the tart pan sides.