Preheat the oven to 180°C. Grease and line the base of a 22cm x 12cm loaf tin.
Place the egg whites and pinch of salt in a large clean bowl and beat with an electric beater until soft peaks form. Gradually add sugar, ¼ cup at a time, beating well between each addition, until the mixture is thick and glossy. Add the vanilla essence and beat until combined.
Combine the plain and self-raising flour. Sift half over the mixture and gently stir to combine. Repeat with remaining combined flour. Stir in the macadamias. Spoon mixture into the prepared tin and bake for 35-40 minutes, until the cake is a caramel colour, feels firm to touch and is slightly cracked in the centre. Don’t let it become too dark, but don’t remove it too early as it may not have set in the centre.
Remove from the oven and allow to cool in the tin for 15 minutes before turning out to cool completely for at least 3 hours. Do not refrigerate or the cake will go soggy.
When the cake is completely cool, preheat oven to 180°C. Use a sharp knife to carefully cut the loaf into thin slices no thicker than 2mm. The thinner, the better. Place the first batch of slices on an oven tray in a single layer and bake, watching carefully for 10-12 minutes, moving the slices on the edge to the centre if necessary, to prevent them from browning too quickly. When the slices are golden, remove from the oven and cool completely on wire racks before storing in airtight containers. Repeat cooking batches with the remaining slices.
These will last for 2-3 weeks if stored correctly.