Prepare and chill the dough.

For the filling, bring the water to a boil in a 3-quart saucepan and remove from heat. Stir in molasses and corn syrup. Stir in baking soda/water mixture (the mixture will foam up in the pan). Set aside to cool. Combine flour and sugar in a mixing bowl and rub in butter until the mixture forms 1/4 to 1/2-inch crumbs. Set aside.

Preheat oven to 400 degrees and set a rack in the lowest level. For the bottom crust, lightly flour the work surface and the dough and roll it to a 12-inch disk. Fold the dough in half and place it in the pan; unfold the dough and press it firmly into the pan. Trim away all but 1/2-inch excess dough at the edge of the pan. Fold excess dough under and flute edge.

Pour cooled molasses mixture into crust and evenly scatter the crumbs over it.

Bake the pie for 15 minutes on the bottom rack of the oven. Lower the temperature to 350 degrees and move the pie to the middle rack. (Place a jelly roll pan lined with aluminum foil on the rack below and under the pie to catch drips if the filling begins to boil over). Bake the pie about 20 to 30 minutes longer, until the crust and crumb topping are a deep golden.