Preheat your over to 375 degrees. Place the pie crust in a 9-inch pie plate and set aside (no need to pre-bake).
Prepare the Liquid Filling:
In a heat safe container (I use a Pyrex measuring cup), add the boiling water and stir in the baking soda.
In a separate bowl, whisk together the molasses, egg, and brown sugar until smooth
Slowly pour the hot baking soda-water mixture into the molasses mixture, stirring constantly to combine evenly. The mixture will be thin and liquidly.
Pour the completed filling into the unbaked pie shell.
Prepare the Crumb Topping:
In a medium bowl, combine the flour, brown sugar, and baking soda. Add the softened butter and cut it in with a pastry cutter or fork until you get a sandy, crumbly texture (like coarse sand - some pea-sized bits are fine).
Sprinkle the crumb mixture evenly over the liquid filling. DO NOT STIR - it will sink in slightly during baking for that signature texture.
Baking:
Bake at 375 for the first 10 minutes, then reduce the heat to 350 degrees and bake for an additional 30-40 minutes, until the topping is golden and the filling is set (it should jiggle just slightly in the center like custard). Let the pie cool completely (at least 2 hours) - this allows the filling to set properly for clean slices and the best texture.
Notes
Tips and Tricks: The baking soda reaction with molasses is key for tenderness and flavor balance - don't skip or reduce the baking soda.Don't overbake; the pie continues to set as it cools. Its okay if there is a little jiggle in the middle and a toothpick inserted should come out mostly clean with a few crumbs.Store at room temperature for up to 4 days (covered loosely.) This pie actually gets better on day 2 as the flavors meld. You can also freeze but the crumbs will soften a bit when thawed - still delicious.Use dark molasses (not blackstrap - it's too bitter and not light molasses as it is too sweet and lacks the robust flavor of classic Shoofly Pie).