Add the flour, brown sugar, cinnamon, butter and salt to a large bowl and cut in together using a pastry knife until the butter is about the size of rice. Set aside.
In a large heat-safe bowl add in the molasses, boiling water, baking soda, and beaten egg until completely combined.
Transfer the mixture and pour it into a pie crust molded pan.
Generously sprinkle on the streusel over the top until it is completely covered.
Bake in the oven at 425° for 15 minutes then at 350° for 20-25 minutes or until firm in the center.
Cool on a rack completely before slicing and serving.
You can add optional toppings such as whipped cream or ice cream.
Make-Ahead: You can make this pie up to 2 days before you slice it.
How to Store: Once the pie has cooled to room temperature, cover with plastic and keep in the refrigerator for 7 days. Likewise, you can cover and freeze for up to 3 months. Thaw for 1 day in the refrigerator before serving.
Most pie tins are 9” and this recipe will fill it all the way to the top. If you are nervous that it will overflow outside of the pan, then reduce the recipe by 25%.
I prefer to use light molasses because the flavor is not as intense and also has less bitterness.
You can make the streusel topping in a food processor instead of using a pastry knife.