Method
1. Pre-heat oven - 175°C/350°F
2. Line 2 clean baking sheets with parchment paper
3. Add plain flour, granulated sugar, baking powder and salt to a clean large mixing bowl
4. Whisk briefly until blended
5. Add unsalted butter and rub in until coarse crumbs form
6. Add egg yolk, buttermilk and vanilla extract to the dough
7. Mix until dough forms
8. Add blueberries to a clean small bowl then set aside
9. Turn out dough on lightly-floured surface and flatten until 1 cm thick
10. Sprinkle blueberries onto dough and press in lightly
11. Fold in thirds and press together lightly
12. Cut into squares
13. Transfer dough to 2 baking sheets
14. Sprinkle with light brown sugar
15. Bake until light golden - 22 min, 175°C