Cube butter and place in freezer while preparing the rest of the ingredients. Keep in freezer no longer than 20 minutes. You want the butter to be chilled but not frozen. 

In a medium bowl, combine the flour, granulated sugar, baking powder and salt. Set aside.

In a separate bowl, whisk together the buttermilk, egg and half of the lemon zest. Set aside.

Remove the butter from the freezer and add to the flour mixture. Using a pastry blender or two forks, cut the butter into the flour mixture until it resembles coarse crumbs. 

Add the wet ingredients to the dry ingredients and combine with a wooden spoon or rubber spatula. Dough will be sticky and a bit crumbly. Toss the blueberries with 1 Tablespoon flour. Fold the blueberries into the scone mixture - be gentle so that you don't smash the berries. 

Turn the dough out onto a floured work surface. Gently press and fold dough together until it comes together in one mass. Flour the dough and your hands as needed so that it is not sticky. Gently press the dough into a 10 inch circle. You can also use a rolling pin, but apply very light pressure.

Cut scones into 12 wedges.

Place on baking sheet lined with parchment about 1 inch apart. Place in refrigerator while preheating the oven to 400°F, about 30 minutes. 

Brush tops of scones with cream. Bake for 20-22 minutes until golden brown.

Leave scones to cool on the baking sheet for 10 minutes before transferring to a wire rack. 

Make the lemon glaze by whisking together the powdered sugar, 4 Tablespoons of milk and the other half of the lemon zest. A thicker glaze will set up better - only use enough milk to be able to drizzle the glaze. 

Drizzle with lemon glaze and let set for about 10 minutes. 

Scones are best served fresh.