Preheat oven to 350 degrees. In a food processor, pulse cookies and sugar until finely ground. Add butter; pulse until crumbs are moistened. Using the bottom of a dry measuring cup, press crumbs into bottom (but not sides) of a 9-inch 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.
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, 45 to 50 minutes. Cool 1 hour at room temperature; refrigerate 1 hour (or up to 1 day).
Unmold tart (if sides stick, gently loosen with a knife). With two thin metal spatulas, transfer to a platter.