• Preheat the oven to 425°F and adjust an oven rack to the middle position.

Prepare Ingredients:

• Wash and dry the blueberries if using fresh berries. Spread out on a paper towel lined plate and place in the freezer. If using frozen berries, do not thaw.
  
• Grate the butter into a bowl and place it in the freezer.
  
• Whisk together the milk and sour cream in a glass measuring cup and place in the refrigerator.
  

Make the Dough:

• Place the flour, sugar, baking powder, salt, baking soda, and lemon zest in a large bowl. Whisk together until well combined. Add the frozen, grated butter to the dry ingredients.
  
• Carefully toss the butter in the dry ingredients to evenly coat the butter. You want to have minimal contact with the butter so it does not melt.
  
• Fold in the milk/sour cream mixture until just combined.
  
• Scrape the dough out onto a flour dusted cutting board. Dust the surface of the dough with flour and knead the dough 6 to 8 times until it forms a ragged ball. Use flour as needed to prevent the dough from sticking.
  
• Roll the dough into a 12 x 12-inch square.
  
• Fold the dough into thirds like a business letter. A bench scraper is helpful for lifting the dough from the work surface.
  
• Fold the dough again into thirds to make a square shape, approximately 4 x 4-iches, and slip it onto a floured plate in the freezer for 5 minutes.
  
• Generously sprinkle the work surface with flour. Roll the dough out into a rectangle approximately 15 inches long and about 10 inches wide. Use flour as needed to prevent the dough from sticking.
  
• Sprinkle the blueberries evenly over the dough and lightly press the berries into the dough.
  
• Carefully roll the dough into a tight log so the resulting roll is 15 inches in length. You may need to use the bench scraper to help lift the dough from the cutting board.
  
• Once the dough is a log, lay it seam side down and press it into a rectangle that is about 15 inches long and about 4 inches wide.
  
• Using a sharp, floured knife to cut the dough into 5 rectangles, cutting the dough approximately every 3 inches of the 15 inch length. Then use the knife to cut each of those rectangles diagonally. This will yield 10 triangles.
  

Add the Topping and Bake:

• Transfer the scones to a parchment lined baking sheet.
• Brush the top of each scone with melted butter.
  
• Sprinkle the tops of the scones with sugar.
  
• Bake the scones for 18 - 25 minutes until golden brown.
  
• Transfer to a wire rack and cool 10 minutes before serving. Serve warm.