Preheat oven to 425 F and line large baking sheet with parchment paper. Set aside. *See notes.
In a large bowl, add flour, sugar, baking powder and salt, whisk well. Add cold butter cut into small pieces and work it into the flour using a pastry cutter or two forks and your hands until small crumbles form.
Add Greek yogurt and vanilla, stir with a spatula and hands towards the end. Then add blueberries, give a few more gentle stirs. Transfer dough onto a floured surface and knead a few more times but handle gently not to squish the blueberries. It helps to tear dough into a few pieces and put back in with blueberries inside.
Roll with a rolling pin into a circle of about 8 inches wide, flat on top and even on edges. Using a pizza cutter or chef's knife, cut into 8 triangles. Separate them carefully and transfer onto previously prepared baking sheet, spacing out.
In a small bowl, whisk the egg with a bit of cold water. Brush on top of each scone (and sprinkle with more sugar optionally) and bake for 20 minutes or until golden brown.
Remove from the oven and enjoy warm!
Video
Notes
*Oven temperature: A few readers have reported the bottoms of scones browning too soon, that's because from leaking sugars from blueberries. I didn't have this problem but all ovens differ, so if you know yours runs hotter bake scones at 400F.
Store: Scones taste best same day. Store under a linen towel for first 24 hours. Keep in an airtight container for 2 more days. After that freeze them.
Freeze: In an airtight container or Ziploc bag for up to 3 months. Thaw on a counter for a few hours. Reheat in a microwave or air fryer for a few minutes. Or bake in the oven at 300 F until warmed through.