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 blended.
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 pea-sized pieces of butter remaining.
04 - In a small bowl, whisk together the heavy cream, egg, and vanilla extract until fully combined.
05 - Pour the wet mixture over the flour-butter mixture. Gently fold with a spatula until just combined, being careful not to overmix.
06 - Gently fold in the blueberries, taking care to avoid crushing them.
07 - Turn the dough onto a lightly floured surface and gently pat into a 7-8 inch circle, about 1 inch thick.
08 - Cut the circle into 8 equal wedges. Place wedges on the prepared baking sheet, spacing them slightly apart.
09 - Brush the tops with extra heavy cream and sprinkle with coarse sugar and a pinch of Vietnamese cinnamon, if desired.
10 - Bake for 18-22 minutes until golden brown and firm to the touch.
11 - Let cool on the baking sheet for 10 minutes before serving warm.