Start by preheating your oven to 420°F. While the oven is warming up, grab a large bowl and add the flour, baking powder, and salt. Sift it together until mixed.
Using your fingertips, massage the butter into the flour mixture until it has a breadcrumb consistency.
Add the sugar and blueberries and stir gently until they're evenly distributed, careful not to overmix.
Add the milk and use your hands to mix the dough together, again careful not to overwork the dough. Once everything is blended, place the dough onto a lightly floured surface and roll until it's 1/4 inch thick.
Lay most of the sliced nectarine slices over half the rectangle, then fold the other half of the dough to cover the nectarines.
Using a knife, cut out three triangles, then cut each unit in half to create six scones.
Place the scones onto a baking sheet lined with parchment paper. Brush each top with a little milk, sprinkle castor sugar on top, then garnish with remaining sliced nectarines.
Bake for 12-15 minutes or until the tops are just golden brown. Remove from the oven and let the scones cool fully on a cooling rack before enjoying.