This recipe is from The Wholesome Home Book:
Shoofly Pie mix 4 cups all purpose flour, 2 cups light brown sugar, 2 teaspoons baking soda.Mix all ingredients.
Additional ingredients and directions for 1 pie
1 cup molasses
1 cup hot water
6 Tablespoons each butter and margarine
Pie crust
Simmer molasses and water together for 1 minute and remove from heat. Measure 3 cups of the mix into a bowl, then cut 6 tablespoons of margarine and 4 tablespoons of the butter into mix until the mixture resembles coarse meal.
Line a pie plate with the crust and sprinkle about 1/3 of the basic mix butter crumbs over the bottom. Pour 1/2 cup of the molasses mixture over the crumbs. Repeat the procedure using about 1 cup crumbs and 1/2 cup liquid until all of the mix and liquid are used, ending with the crumbs. Dot with the remainder of the butter and bake in preheated oven 375 deg for 50 minutes. Serve warm or at room temperature.
I think I see why this pie isn't so popular now.