In a large bowl, rub together the sugar and lemon zest to release the oils.
Add the flour, baking powder, baking soda, and salt. Whisk to combine.
Grate very cold or frozen butter on a box grater (or cut into cubes and rub in with your hands or a pastry cutter) until the mixture resembles coarse crumbs.
Gently mix in the blueberries to coat them in flour.
Add the buttermilk and mix lightly to bring the dough together. It should still look a little rough.
Tip the dough onto a floured surface. Knead very gently to form a thick rectangle or round disc. Do not overwork the dough.
Cut into 8 large or 10 smaller triangles or squares.
Place on a lined baking tray with space between them. Brush the tops (not the sides) with buttermilk and sprinkle generously with brown sugar.
Chill the tray in the fridge while you preheat the oven to 200°C (400°F).
Bake for 20 to 25 minutes until golden brown on top.
