Take about 2 litres of milk (8 glasses)
Boil it and while it is boiling add either lemon or vinegar
After all the milk has curdled and only a watery base is remained
Drain the water out and take the curdled milk and add about one fourth portion sugar of the total portion of the curdled milk.
Mix it in mixer ...and then flavor it as u like it
Different flavorings can be
add chopped oranges
chopped strawberries
whatever flavoring u add after that mix it again and add a little of the watery base
to that

After that pour it in a baking dish and freeze it for about 2/3 hours to let it set
And hey presto u have Sandesh an Indian Bengali dessert.