Pour the washed berries with water (0.5 cups) and boil. Soak gelatin in the remaining water until it swells. While hot, wipe the blackberry through a sieve. Add sugar to hot mashed potatoes, mix thoroughly. Warm up the swollen gelatin over a low heat in a water bath until the crystals are completely dissolved. Combine gelatin with mashed berry. Beat mashed potatoes with a gelatin mixer, at low speed, until a stable foam. Pour the condensed milk and whisk again. We lay out on the forms and let it freeze. Decorate with berries on top, if desired. Blackberry soufflé with condensed milk is ready! Enjoy your meal!