Preheat oven to 200°C. Lightly coat a large baking tray with non-stick cooking spray.
Combine the flour, ¼ cup sugar, baking powder, salt and bicarbonate of soda in a food processor. Pulse to combine. Add ginger; pulse until finely ground. Add butter; pulse until the mixture resembles coarse polenta. Transfer to a medium bowl.
Grate carrot in food processor. Add to flour mixture. Fold buttermilk into flour mixture just until evenly moistened.
Scrape dough onto a floured work surface. Knead briefly just until dough holds together. Pat out to a 2.5 cm-thick round. Sprinkle top with remaining 2 tsp sugar.
Cut dough into 8 equal wedges. Arrange 2.5 cm apart on the prepared baking tray. Bake until golden, 18 to 20 minutes. Transfer to a wire rack to cool.
Scones are traditionally made with butter, sugar, eggs and cream. Here, the eggs are omitted and buttermilk stands in for cream to cut back on the saturated fat content.