How to Make It
Preheat oven to 350° F. In a food processor, pulse flour, sugar, butter, and salt until crumbly; set aside.
Whisk together molasses and boiling water; whisk in egg and baking soda.
Pour the molasses mixture into the piecrust, top with the flour mixture, and bake until the center is set, 40 to 50 minutes. Let cool before serving.