Arrange rhubarb in the bottom of a 9-inch pie plate. Sprinkle with remaining filling ingredients.
Topping: Sift together the flour, sugar, salt, and baking powder; cut in shortening until mixture looks like meal. Mix together beaten egg and milk; stir into flour mixture until dry ingredients are moistened. Drop dough by tablespoons over rhubarb mixture; spread dough together with a spatula.
Bake at 350° for 35 minutes, or until topping is lightly browned and filling is bubbly.