Here you check how to make bori at home:
Urad Dal – 250 gm
Soak urad dal overnight or minimum 4 hours. Now clean dal and make a smooth paste in a grinder. Take out the paste and beat well. Also check the consistency of the paste. It should not be either watery or very thick. Take a clean thin cotton cloth (I used a old cotton saree) and place it on a sunny bright place. Now place one one drop paste on it using fingers maintaining a row or column. Allow it to dry on sunlight.
If it is not dried in one day, next day again keep it on sunlight. Once they are dried , will come out from the cloth or you can turn each bori and allow to dry the back side. After drying store them in a air tight container.
N.B: Try to prepare bori in summer or winter season when you get proper sunlight. If they are not dried properly, fungus contamination might happen.