Combine 1 cup blueberries with 1 1/4 cups water and the cup of sugar in a saucepan and bring to a boil. Mix the cornstarch with the 1/4 cup of water and stir into blueberry sauce. Cook slowly until thick and clear. Add lemon juice and allow to cool. Then add the remaining 3 cups of berries. Chill in refrigerator.
