Preheat oven to 375 degrees F. Have ready a 9 inch unbaked deep dish dough-lined pie plate, and set it on a rimmed baking sheet.
Mix flour, brown sugar, cinnamon, nutmeg and salt together in a mixing bowl.
Add shortening to the flour mixture and mix until coarse and crumbly. Measure out 1/2 cup of the flour mixture and set aside for topping.
Make a well in the crumb mixture in the mixing bowl. Put the egg and molasses in the well, mix those two together, then drag in all the flour mixture and blend everything.
Pour 3/4 cup of boiling water over the flour mixture and stir until evenly blended. Next, channel your inner 5 year old and add the baking soda. Stir and watch the magic! The mixture will become fizzy and light.
Pour your fizzy filling into the pie shell. Again, make sure it is sitting on a rimmed baking sheet.
Sprinkle the reserved 1/2 cup of crumb mixture over the liquidy pie filling.
Bake in a preheated 375 degree oven for 45 minutes. Let cool for about 4 hours or so. When you cut it, you should have two very distinct layers -- a top layer of cake and a soft molasses flavored layer.