Preheat the oven to 190 degrees C. Sift together the plain flour, cake flour, baking powder and bicarb soda; set aside.
In a large bowl, cream together the butter, white sugar and brown sugar until smooth. Beat in the eggs and vanilla until well blended. Gradually stir in the flour mixture. Stir in the chocolate chips and Brazil nuts. Drop biscuits by rounded tablespoonfuls 5cm apart onto ungreased baking trays.
Bake for 10 to 14 minutes in the preheated oven until the edges are light brown. Let biscuits cool on the baking tray before removing to wire racks to cool completely.