Preheat the oven to 425 degrees F.
Cube the butter and place it into the freezer to chill until you're ready to make the dough.
In a large bowl, whisk the flour, sugar, baking powder, baking soda, and salt together.
Mix together the wet ingredients and place into the fridge to stay cold.
Cut the butter into the flour using a pastry blender, food processor or your fingertips. If using a food processor, combine the butter with the flour on low speed. You don't want the butter to melt from too fast of force! When you're done, the mixture should look like small coarse pebbles, and should feel like slightly damp sand.
Gradually add the buttermilk mixture to the flour mixture as your food processor is pulsing on low. Stir just until the dough comes together. The dough should be sticky, but should still cohesively coat the blade and hold a shape.
Transfer the dough to a bowl and add the blueberries. Delicately fold in.
Flour a clean surface and transfer your dough onto the floured surface. Sprinkle flour on top of the sticky dough ball, then roll each side of the dough in flour. Knead the dough by folding it onto itself, about 5-10 times. If it begins to stick to the cutting board, lightly flour so that it doesn't stick. Once a ball is formed, stop kneading. Do not over knead the dough, if it holds a shape and is not sticky on the sides, you’re good! It should feel soft and pillowy, like if you ripped it apart it would still be as sticky as how it was when you took it out of the food processor.
Roll out the dough with a rolling pin until about 1/2 inch thick around the edges.
With a knife or benchscraper, slice the dough into 8 equal triangles.
Place the scones on a cutting board and cover with parchment paper. Freeze for 15 minutes.
Remove the scones from the freezer, then brush with egg wash and top with coarse raw turbinado sugar.
Bake for 15 minutes on the 2nd to top rack in the oven, and check up on them halfway through. If scones on one side are more browned than the other, rotate the pan so the heat will distribute evenly and cook them to equal doneness.
Remove the scones from the oven and let them cool for 10 minutes. Plate and serve immediately, or store in a sealed plastic bag at room temperature for up to 2 days! Serve with honey miso butter, of course :)