Position a rack in the lower third of your oven. Preheat the oven to 425°F (218°C) . Line a baking sheet with parchment paper.
Prepare pie crust, roll and place into a 9-inch pie plate. Freeze for 30 minutes (this helps with keeping crust from puffing up while baking).
Cover the crust with parchment paper or foil and fill with pie weights. Bake in oven for 15 minutes. Remove from oven and remove parchment and weights. Do NOT prick bottom. Bake for an additional 5 minutes. Remove from oven and cool while you make topping and filling.
Increase oven heat to 450oF (230°C).
Combine flour, brown sugar, cinnamon, and nutmeg in a medium bowl.
With a pastry cutter or your fingertips, cut in butter until mixture resembles coarse crumbs. Set aside.
Combine molasses, hot water, and baking soda together in a medium bowl. Pour mixture into pie shell.
Sprinkle the brown sugar mixture on top of pie filling.
Place pie on the cookie sheet and bake in lower third of your oven in the preheated oven for 15 minutes. Lower temperature to 350℉ (175℃); bake for an additional 20-25 minutes until the pie filling is set and firm. If the crust edges are browning too much, cover with a pie shield to keep from burning.