To make the scones, preheat oven to 180°C. Line a baking tray with baking paper. Place macadamias into the bowl of a food processor and add combined flour, sugar, baking powder and salt. Pulse until the macadamias are almost finely chopped and the mixture resembles a coarse flour. Do not over-process or the mixture will stick together; the nuts do not need to be completely ground.
Place the mixture into a large bowl, add butter cubes and, using your fingertips, rub in the butter until the mixture is the consistency of coarse crumbs. Add the milk and finely chopped macadamias and gently combine to form a ball. (You could add sultanas or spices at this stage if desired).
Gather the dough and knead gently to make a smooth round. Pat the round down to a disc about 2-4 cm thick. Use a scone cutter to cut scone shapes. Reroll remaining dough and repeat until all the dough is used and you have 8-10 scones.
Place the scones on the prepared tray and brush with a little of the extra milk. Bake for 10-12 minutes until the scones are puffed and golden.
For the berries, combine the sugar and water in a small saucepan and stir over medium heat to dissolve sugar. Bring to the boil, add the blackberries, reduce heat to low and simmer for 2-3 minutes, gently stirring occasionally. Allow the berries to cool in the juice for 10 minutes.
Serve the scones warm with the blackberries and whipped cream.