Pour melted 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.
To prepare filling: 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 to 50 minutes. Cool for 1 hour at room temperature; refrigerate for 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.
Nutrition information per serving:
Calories250Fat13 gCarbohydrates32 g
Saturated fat8 gProtein3 gDietary fiber3 g