Preheat oven to 200°C (400°F) and line a baking sheet with parchment paper
In a large bowl, whisk together flour, baking powder, baking soda, salt, and sugar
Add cold cubed butter and use a pastry cutter or your fingers to mix until the mixture resembles coarse crumbs
Pour in cold buttermilk and gently fold until dough comes together, being careful not to overmix
Add blueberries and lightly fold to distribute them evenly
Turn the dough onto a floured surface and pat into a 1-inch thick rectangle
Cut into 2–3 inch rounds using a biscuit cutter or a glass and place on prepared baking sheet
Bake for 18–20 minutes, until golden brown on top, then remove and let cool slightly
While biscuits are cooling, whisk together powdered sugar, milk, and vanilla until smooth
Drizzle glaze over warm biscuits and serve immediately
