Begin by washing the dal properly, and then soak it for at least six hours, and more if necessary. Once that's done, grind the dal in processor really well. Make sure there's not too much water in it though. The idea is to get a thick paste-like dough.
Now take the salt and the kalonji and add it to the paste. You need to whip the mixture hard, use a hand mixer, so that the batter becomes light.
In the older days, these boris were made by hand - taking a little mixture and making tear drop shapes on a newspaper and putting them out in the sun to dry. You can of course use an icing bag with a round nozzle. If a newspaper is too passé for you, use a metal tray and brush it with some oil so it doesn't stick.
It takes a whole day in the sun for the dumplings to dry; keep it out for longer if it takes time.
When it's ready it should be completely dry; crush one in your hand if it crumbles easily, it's done. You can store these in an airtight container for a few days.
To cook with it, you need to gently sauté it in oil before adding it in anything.
Bengali Dal Bori keeps well for a year or two if you store them n a cool, dry place.
The recipe can be made of both Masoor and Moong dal, in both the cases use skinned dal. Use the same procedure while using Moong as well.