In a large bowl, combine the flour and baking powder and stir together with a large fork. Use the large holes on a box grater to grate the frozen butter directly into the dry ingredients. Stir together with a fork and set aside.

Combine the milk, the white sugar and the salt in a medium bowl and whisk together.

Make a well in the center of the dry-butter ingredients and add the milk mixture. Stir together with a fork, adding enough flour or milk as needed until large clumps form and the dough just comes together.

Sprinkle a pastry mat, wooden cutting board or wax paper with flour. Turn the dough out onto the surface and pat a few times with your hands until it loosely holds together.

Use a bench scraper or a large knife to divide dough in half. Stack one half on top of each other, then roll into another rectangle, sprinkling the surface with flour if it gets too sticky. Repeat the process two to three more times before patting it into one final rectangle.

Wrap the dough in plastic wrap and refrigerate for at least 2 hours and up to overnight.

Preheat oven to 400F. Line a baking sheet with parchment paper. Place a shallow pan of water on the bottom rack of the oven for steam.

Sprinkle a pastry mat, wooden cutting board or wax paper with flour. Turn the dough out onto the surface.

Use a bench scraper or very sharp knife to trim the edges of the rectangle. Use a square cookie cutter or a knife to cut the remaining dough into squares, about 2 inches each.

Remove the cut scones to the baking sheet lined with parchment paper, placing them close to each other. Freeze until cold, about 15 minutes.

Spray the tops of the scones with cooking spray, or brush with melted butter, sprinkle the tops with sugar and flakey salt, and place in oven.

Bake for 25-30 minutes, until golden brown. When pulled away from others, the edge should look baked all the way through.