Shoofly Pie

On a floured surface, roll dough to fit a 9-in. deep-dish pie plate. Trim and flute edge. Refrigerate at least 30 minutes., Meanwhile, preheat oven to 425°. For filling, mix brown sugar, molasses, egg, flour and baking soda. Gradually stir in boiling water; cool completely., Line unpricked crust with a double thickness of foil. Fill with pie weights, dried beans or uncooked rice. Bake on a lower oven rack 15 minutes. Remove foil and pie weights; brush crust with egg yolk. Bake 5 minutes. Cool on a wire rack. Reduce oven setting to 350°., In another bowl, whisk together first four topping ingredients. Cut in butter until crumbly. Add filling to crust; sprinkle with topping. Cover edge of pie with foil., Bake until filling is set and golden brown, 45-50 minutes. Cool on a wire rack. Store in the refrigerator.