In a small bowl combine flour, baking powder and salt; set aside. In a large bowl; combine butter, sugar, brown sugar and vanilla essence; beat until creamy. Beat in eggs. Gradually add flour mixture; mix well. Stir in chocolate chips. Drop by rounded level teaspoons onto greased baking tray. Bake for about 12 minutes until just turning brown round the edges. Allow to cool.
In a saucepan combine sugar, cocoa, milk, butter and salt. Bring mixture to a rolling boil, stirring constantly for 2 minutes. Remove from heat and add vanilla then continue beating until icing starts to thicken slightly. The icing will be very creamy.
Using a piping bag or a spoon, place icing on the bottom of one biscuit then top with a second. Enjoy.