Combine the sugar, cornstarch and sweetener, pressing out all lumps. Dump the blueberries into a 6-cup shallow casserole that has been lightly sprayed with nonstick vegetable cooking spray. Dump in the sugar mixutre, add the lemon juice, and toss well to mix. With a potato masher, lightly mash the blueberries, set aside. Butter the bread,(with the margarine) lightly on one side, stack the slices and cut into 1 cm cubes.Dump into the casserole and toss well to mix. Bake the pudding uncovered in a moderate 180ºC oven for 30 minutes, remove from oven, add the evaporated skim milk and stir well to mix. Return to to oven and bake uncovered for 15 minutes.Serve warm, topped, if you like, by a little whole milk. Makes 6 servings.