Preheat oven to 170°C. Lightly grease, flour and line the base of a 20–22cm springform cake pan.
Place flour, macadamias and chocolate in a food processor and pulse on and off until mixture is a coarse crumb.
Beat egg whites until soft peaks form. Gradually add sugar, beating until mixture is thick and glossy. Lightly fold egg whites through macadamia mixture with zest.
Spoon into prepared pan and bake for 30–40 minutes or until a skewer inserted in the centre comes out clean. Allow to cool in tin for 5–10 minutes before lifting gently onto a wire rack to cool completely.
TIP: This is great on a cold night served hot out of the oven with caramelised oranges and Crème Fraiche.