Beat butter and brown sugar in a small bowl with an electric mixer until smooth and creamy. Beat in the egg and treacle. Combine the flour, ground ginger, bicarbonate of soda and salt and stir into the butter mixture. Add the fresh and crystallised gingers, cover and refrigerate for 2 hours.
Preheat oven to 180C. Shape dough into 2.5cm balls and place 5cm apart on ungreased baking trays.
Bake for 10 minutes or until lightly browned. Cool on wire racks.