Preheat oven to 400 degrees F.
Prepare pie pastry. Using a floured rolling pin, roll pastry 2 inches larger than an inverted pie plate. Fold pastry into quarter folds and ease into pie plate, pressing firmly against bottom and side; set aside.
In a large bowl, using a pastry blender or two knives, cut shortening or butter into flour, brown sugar, and salt until mixture is crumble and particles are the size of small peas; set aside.
In a large bowl, add baking soda and hot water; stir until baking soda is dissolved. Add molasses (or molasses and corn syrup combination) and egg; beat until well blended. Pour into prepared unbaked pie shell, filling half full (you may not need to use all of the filling - if you overfill the shell, it will overflow during baking). Trim overhanging edge of pastry 1/2 inch from rim of plate.
Gently sprinkle prepared crumb mixture evenly over top of the pie (crumbs will both partly sink and partly float).
Bake 10 minutes and then reduce oven to 350 degrees F. Bake an additional 35 to 40 minutes or until the internal temperature registers at least 160 degrees F. on your cooking thermometer and a knife inserted in center comes out clean
Remove from oven and cool on a wire rack before serving. This pie is best served at room temperature.
Makes 8 servings.
* Can substitute 1/2 cup dark molasses and 1/2 cup light or dark corn syrup.
Wet Bottom Shoofly Pie Recipe: https://whatscookingamerica.net/desserts/shooflypie.htm