Preheat oven to 150 degrees C. Line baking trays with baking paper.
In a medium bowl, cream together the butter and brown sugar. Stir in the egg and vanilla until smooth. Sift together the flour, salt and bicarb soda, stir into the creamed mixture. Then stir in the rolled oats and macadamias. Finally, stir in the crushed toffee pieces.
Drop dough by rounded tablespoons onto the prepared baking trays and flatten slightly. Bake for 10 to 18 minutes in the preheated oven. Biscuits will have a dry appearance when finished baking.