Preheat the oven to 425˚F. Cut a piece of parchment paper to fit a half sheet pan
Whisk together the flour, sugar, baking powder, salt and optional chopped lemon balm in a mixing bowl
Cut the cold butter into small cubes and mix it into the flour mixture using your hands. Press the butter chunks between your fingers to cut them into the flour mixture lifting your hands up as you go to aerate the mixture. The resulting mixture should be sandy and resemble coarse breadcrumbs.
Mix the buttermilk, egg, lemon zest, and vanilla extract together in a separate bowl then pour the wet mixture into the dry mixture, leaving behind about 2 tablespoons of the wet mixture to brush the scones with later.
Use your hands to mix the dough. It should be dry but hold together when squeezed. If it is too dry, mix in 1 tablespoon more buttermilk at a time until it holds together.
Lightly flour the piece of parchment paper and dump the crumbly scone dough out onto it. Bring the dough together and press it into a large rectangle. A bench scraper is helpful here.
Reserve a quarter of the blueberries to use later, then add another quarter of the blueberries to the dough so that they evenly cover the bottom half of the rectangle.
Use a bench scraper to help fold the top half of the dough over to cover the berries. Then turn it a quarter-turn (90˚) and press it back out into a larger rectangle. Lightly flour the dough, surface, and your hands as needed. The purpose of this technique is to gently fold in the fruit and create flaky layers in the scones.
Repeat layering the blueberries and folding the dough 2 more times until 3/4 of the berries are incorporated. So the dough will be folded a total of 3 times with 1/4 of the berries being folded each time.
Press the dough into a circle about 8” wide and 1” thick. Gently press the remaining blueberries into the top and then cut the circle into 6 wedges.
Transfer the scones on the parchment paper to the sheet pan and space them about 1" apart from each other. Brush the tops with the saved wet mixture. Sprinkle about ½ teaspoon of sugar onto the top of each scone.
Bake at 425˚F for 25-30 minutes until the scones are golden brown and feel crusty on the outside but still soft in the middle when pressed.
Let them cool on the pan for 5 minutes then serve warm.