1. Place the dark chocolate in a heatproof bowl over a saucepan of simmering water, ensuring the bowl doesn't touch the water. Stir until the chocolate has melted. Set aside, stirring occasionally, until cooled to room temperature.

2. Cream the butter and sugar in a large bowl using electric beaters until pale and fluffy. Add the eggs one at a time, beating well after each addition. Beat in the cooled, melted chocolate. Sift in the flours, add the milk chocolate and white chocolate and, using a wooden spoon, stir to combine. Cover with plastic wrap and refrigerate for 1 hour, or until firm enough to roll.

3. Preheat the oven to 180°C. Line a baking tray with baking paper.

4. Roll tablespoons of the mixture into balls, place on the prepared tray 5cm apart and flatten slightly. Bake for 10 minutes, or until the cookies are still slightly soft to touch. Allow to cool on the tray for 5 minutes, then transfer to a wire rack to cool completely. Repeat with the remaining mixture.

Note: These cookies will keep, stored in an airtight container, for up to 1 week.