Step 1

With the rack in the highest position, preheat the oven to 425°F (210°C). Line two baking sheets with silicone mats or parchment paper.

Step 2

In a food processor, combine the flour, sugar, baking powder, baking soda and salt. Add the butter and pulse until the butter forms pea-sized pieces. Add 1 cup (250 ml) of the buttermilk, and pulse until just blended.

Step 3

On a lightly floured work surface, using a rolling pin, roll out the dough into a 16-inch (45 cm) square. Arrange the blueberries over the dough. Roll the dough into a long cylinder and press it flat to a thickness of 1 1/4 inches (3 cm) while keeping it 16 inches (45 cm) long. Cut the dough into 7 rectangles, then cut each rectangle diagonally into triangles. Place on the prepared sheets, or freeze at this point.

Step 4

Brush the scones with the remaining buttermilk and sprinkle with the coarse sugar.

Step 5

Bake one sheet at a time for 18 minutes or until the scones are golden brown. (Bake frozen scones for about 23 minutes.) Let cool.