Preheat oven to 180ºC. Heat cream in a non-stick pan and bring to a boil. Put chocolate in a Borosil Mixing Bowl, pour the hot cream over it. Mix well till the chocolate melts, cover with a cling film and refrigerate. Cream together butter and castor sugar in another bowl till light and fluffy. Add egg and vanilla essence and beat well. Sieve together flour, cocoa powder and baking powder into the butter-sugar mixture and fold until well combined resulting in a dough. Roll out the dough into a thin sheet. Cut out small discs using a cookie cutter. Place half the discs on a baking tray. Remove the cling film and divide the chocolate mixture into equal portions and shape them into small balls. Place the balls on the discs placed on the tray and cover with the remaining discs. Press and refrigerate for five to ten minutes. Put the tray in the preheated oven and bake for ten to fifteen minutes. Remove from heat and cool.