Wash hands with soap and water for 20 seconds.
Whisk flour, sugar, lemon zest, baking powder, and salt together in a large bowl. Grate the frozen butter and add it to the flour mixture. Combine with a pastry cutter, two forks, or your fingers until the mixture comes together in pea-sized crumbs. Place in the refrigerator or freezer as you mix the wet ingredients together. Whisk 1/2 cup milk, the egg, and vanilla extract together in a small bowl. Drizzle over the flour mixture, add the blueberries, then mix together until everything appears moistened.
Do not taste or eat any raw dough or batter made with uncooked flour and/or raw eggs.
Pour dough onto the counter and, with floured hands, work into a ball. Dough will be sticky. If it’s too sticky, add a little more flour. If it seems too dry, add 1-2 more Tablespoons milk. Press into an 8-inch disc and, with a sharp knife, cut into 8 wedges. Brush scones with remaining milk.
Place scones on a plate and refrigerate for at least 15 minutes.
Preheat oven to 400°F.
Line a large baking sheet with parchment paper or silicone baking mat. After refrigerating, arrange scones 2-3 inches apart on the prepared baking sheet(s).
Bake for 22-25 minutes or until golden brown around the edges and lightly browned on top. Remove from the oven and cool for a few minutes before topping with lemon icing.