01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large bowl, whisk together the flour, sugar, baking powder, salt, and Vietnamese cinnamon until well combined.
03 - Add the cold cubed butter and cut it into the dry ingredients using a pastry cutter or your fingers until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
04 - In a small bowl, whisk together the heavy cream, egg, and vanilla extract until fully incorporated.
05 - Pour the wet mixture over the flour-butter mixture. Gently fold until just combined. Add the blueberries and fold carefully to avoid crushing them. The dough should be slightly sticky but manageable.
06 - Turn the dough onto a lightly floured surface and pat into a 7-8 inch circle, about 1 inch thick. Cut into 8 equal wedges and place them on the prepared baking sheet, spacing about 2 inches apart.
07 - Brush the tops with extra heavy cream and sprinkle with coarse sugar and a pinch of Vietnamese cinnamon, if desired.
08 - Bake for 18-22 minutes until golden brown and firm to the touch. Rotate the baking sheet halfway through for even browning.
09 - Let scones cool on the baking sheet for 10 minutes before transferring to a wire rack. Serve warm or at room temperature.