How to Make It
Prepare the Biscuits: Preheat oven to 475°F. Brush a 10-inch cast-iron skillet with 1 tablespoon of the melted butter.
Whisk together flour, sugar, and salt in a large bowl until combined.
Using a box grater, grate the frozen butter into the flour mixture, and lightly toss to coat butter with flour. Fold blueberries into flour mixture until evenly distributed. Gently stir in buttermilk with a wooden spoon until dough is formed. Do not overmix.
Transfer dough to a lightly floured surface. Lightly sprinkle flour over top of dough. Using a lightly floured rolling pin, roll dough into a 3/4-inch-thick rectangle (about 9 x 5 inches). Fold dough in half so short ends meet. Repeat process 1 more time.
With a floured 2 1/2-inch round cookie cutter, cut out biscuits and place in buttered cast-iron skillet. Use the leftover scraps to make 1 more biscuit, and add to skillet. Bake in preheated oven until tops are golden, about 15 minutes. Brush tops of biscuits with remaining 2 tablespoons melted butter. Let cool 5 minutes in skillet.
Meanwhile, prepare the Glaze: Stir together powdered sugar and lemon juice in a small bowl until smooth. Drizzle glaze on top of biscuits and serve.