Mix cocoa and milk powder together. Add half cup milk, and dissolve, to make a smooth paste. Put butter and brown sugar in a nonstick pan. Place on low heat, stirring occasionally, till fully melted. Add remaining milk, bring to a boil. Add prepared paste, gradually pouring, while stirring continuously. Cook while gently stirring, to form a very soft lump. Mixture should leave sides of pan easily. Add in vanilla essence, rice crispies and half the wheat bran. Take off fire, mix well, off the fire ,till the temperature of mixture lowers, for handling. Roll into small balls between both palms. Roll these balls in the remaining bran, to coat all over. Refrigerate on a sheet of butter paper, till well set. Store refrigerated in airtight container.