Rinse the prunes, leave to soak for several hours in water sweetened with sugar. Cook until soft. Remove the stones. Press prunes into a pulp. To make the pastry, mix the baking powder with the flour and add the stiffly beaten cream. Mix as quickly as possible and finally add the melted butter. Leave the pastry to harden in a cold place. Roll out the pastry on a floured surface to about 1/4 inch thick. Cut into squares about 3 inches in size. Put a teaspoon of filling in the center of each piece. Split the corners and fold other strip to meet in the middle. Beat a whole egg and brush on cookies. Bake in a very hot oven at 475° for only a few minutes.