Whisk together molasses and melted butter, then add to the cookie crumbs. Stir well to combine.
Dump crust mixture into an ungreased 9" pie pan.
Spread mixture evenly over the bottom and sides of the pan, pressing gently but firmly to compact the crumb mixture into a crust.
Bake for 10 minutes, allow to cool fully before making the filling.
Gingerbread Custard Filling:
In a large mixing bowl, whisk eggs together with brown sugar until fluffy and pale. Add cornstarch, spices, and salt, whisk until incorporated and smooth. Set aside.
In a small saucepan, whisk together whipping cream, milk, and molasses. milk. Heat over medium heat, just to the start of a boil.
Measure about ¼ cup of the cream mixture, and stream slowly into egg mixture while whisking. Continue streaming liquid and whisking until it is completely incorporated, and mixture is smooth. Repeat with another ¼ cup of hot cream.
Remove saucepan from heat, pour remaining egg mixture into cream mixture, whisking constantly. Once fully incorporated and smooth, return to heat.
Turn heat to medium-low. Continue whisking mixture constantly, cooking until mixture is very thick.
Remove from heat, whisk in butter and vanilla extract until butter is melted and the mixture is smooth.
Cool to room temperature.
Whisk filling again, pour into the cooled crust, cover with plastic wrap. Chill for 2 hours.
Vanilla Whipped Topping & Assembly
Sprinkle gelatin over the cold water in a small bowl and let it absorb for five minutes.
Combine heavy whipping cream, powdered sugar, and vanilla extract in a mixing bowl (if using an electric mixer), or in the bowl of a stand mixer fit with a whisk attachment.
Whip on medium speed until soft peaks start to form.
Transfer gelatin mixture to the microwave. Heat in 10 second increments until the gelatin dissolves into the water.
Fold gelatin mixture to cream mixture, then whip until stiff peaks form.
Spread whipped topping over the chilled pie, or pipe rosettes around the border.
Sprinkle with cinnamon if desired,, chill another 2 hours to set the whipped cream.