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 to the dry mixture. Use a pastry cutter or your fingers to work the butter into the flour 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 with a spatula until just combined. Be careful not to overmix.
06 - Gently fold in the blueberries, taking care to avoid crushing them. If using frozen blueberries, do not thaw first.
07 - Turn the dough onto a lightly floured surface. Pat gently into a 7-8 inch circle, about 1 inch thick. Do not knead.
08 - Cut the circle into 8 equal wedges using a sharp knife. Place the wedges on the prepared baking sheet, spacing them slightly apart.
09 - Brush the tops of each scone with extra heavy cream. Sprinkle with coarse sugar and a pinch of Vietnamese cinnamon if desired.
10 - Bake for 18-22 minutes until golden brown on top and firm to the touch. Rotate the baking sheet halfway through for even baking.
11 - Let the scones cool on the baking sheet for 10 minutes before serving. Serve warm or at room temperature.