Preheat your oven to 400 degrees. If you're using a homemade pie crust, prepare it and place it in a 9-inch pie dish.
If using a store-bought crust, ensure its thawed if frozen, and place it in the pie dish.
In a medium-sized mixing bowl, combine flour, brown sugars, cinnamon, nutmeg, ginger, and salt.
Cut in the cold butter using a pastry cutter or two knives until the mixture resembles coarse crumbs.
In a separate small bowl, dissolve the baking soda in hot water. Stir in the molasses until well combined.
Pour the molasses mixture into the prepared pie dish.
Sprinkle flour mixture over the filling into the pie dish.
Place the pie in the preheated oven and bake for 10 minutes.
After 15 minutes, turn oven to 350 degrees, and continue baking for 30 more minutes, or until the filling is set and the crust is golden brown.
Once baked, remove the pie from the oven and allow it to cool on a wire rack for at least 20 minutes before serving.
Serve slices with whipped cream or vanilla ice cream if desired.