Preheat oven to 220°C (200°C fan-forced). Grease 20cm x 30cm lamington pan.
Sift flour and sugar into large bowl; rub in butter with fingertips. Add chocolate and blueberries.
Make a well in centre of flour mixture; add buttermilk and almost all the water. Use a knife to "cut" water and buttermilk through the flour mixture, mixing to a soft sticky dough.
Press dough out to 2cm thickness. Dip 4.5cm round cutter in flour; cut as many rounds as you can from piece of dough. Place scones, side by side, just touching, in pan.
Gently knead scraps of dough together; repeat pressing and cutting of dough, place in same pan. Brush tops with a little extra milk; bake for about 15 minutes, or until scones are just browned and sound hollow when tapped firmly on the top with fingertips.
Serve with blueberry jam and cream. The scones are suitable to freeze.