1Combine 2 cups flour, brown sugar, baking powder, and salt in a bowl. With a pastry blender, cut in the margarine until the mixture resembles coarse crumbs. Stir in the evaporated milk and beaten egg.
2Press the dough into the bottom and partly up the sides of a 9x13-inch baking dish. For a thicker crust, press the dough into the bottom of the pan only.
3Preheat an oven to 350 degrees F (175 degrees C).
4Mix the rhubarb, gelatin mix, and 1/2 cup of white sugar. Spread the fruit over the dough. Combine the remaining 1/2 cup white sugar, 1 cup of flour, and softened butter in a bowl. Cut in the butter until the mixture resembles coarse crumbs. Top the rhubarb with the streusel mixture.
5Bake in the preheated oven until the topping is golden brown and the filling is bubbly, about 45 minutes.
Footnotes
Cook's Note
You can substitute strawberry gelatin for the raspberry, if you prefer.
Editor's Note
Making the crust can also be done in a food processor. In Step 1, pulse the margarine and flour mixture in food processor until it's the size of small peas. Turn mixture into a bowl, and proceed with recipe.