Cut the butter up into chunks, place on a plate and put in the freezer for 30 minutes to 1 hour.
Place butter and dry ingredients into a food processor and pulse until the butter is in small, pea-sized chunks.
Add sourdough starter and vanilla extract. If the dough is dry, add 1-2 tbs of cold milk or water. Start with 1 tbs and determine if it needs more. Pulse until it begins to form a ball.
Add the dough to bowl and fold in blueberries and lemon zest (the blueberries may pop which is okay).
Preheat the oven to 425 degrees Fahrenheit.
Place the dough on a piece of parchment paper. Roll it out on the sheet into a square about 1-2 inches thick.
Cut scones into 8 even triangles then place onto a lined baking sheet with space between each.
Create an egg wash by cracking an egg into a small bowl and whisking it thoroughly. Brush egg wash onto the top of each scone and sprinkle with sugar on top.
Place scones in the oven and bake for 15-20 minutes.
Gums, oils, fillers—and everything else on their labels—don’t belong in milk, or your body. We leave them out on purpose because it tastes and feels better without them.
