In a medium mixing bowl, combine the flour, sugar, salt, baking soda, and baking powder. Stir gently to mix well.

Add the cold, cubed butter to the flour mixture. Using your fingers, work the butter into the flour until it resembles large peas.

Toss in the fresh blueberries gently, being careful not to crush them.

In a measuring cup, whisk together the buttermilk, egg, and vanilla extract until well combined.

Make a well in the center of the flour mixture and pour in the wet ingredients, reserving about 2 tablespoons for an egg wash later.

Use a spatula or wooden spoon to fold the mixture together, forming a wet dough.

Turn the dough onto a well-floured surface, fold it over itself 2-3 times to lightly knead, then shape it into a circle about 1.5 inches thick.

Use a sharp knife or a pizza cutter to cut the dough into 8 equal wedges.

Place the scones on a lined baking sheet and either freeze or refrigerate them while the oven preheats to 400°F (200°C).

Brush the tops and sides with the reserved egg wash, and sprinkle generously with turbinado sugar.

Bake in the preheated oven for 23-24 minutes until golden brown and a toothpick inserted comes out clean.

Allow the scones to cool completely on a wire rack before serving.