Preheat oven to 450F. In a large mixing bowl mix together flour, sugar, baking powder and salt. Using a cheese grater, grate frozen butter into the bowl.

Gently mix the butter into the dry ingredients with clean hands until its evenly distributed. Pour the milk into the bowl and gently mix with a wooden spoon. Do not overmix! You want the dough to be crumbly.

Dump dough onto a lightly floured counter top. Using your hands, gently press into a circle that is about 3/4 inch thick.

Use a large cookie cutter or biscuit cutter (about 3 1/4 inch in diameter) to cut out biscuits. Do not twist when you cut the biscuits just press down and up. 

You should get about 7 biscuits. You can gently push scraps together to cut out more. Arrange biscuits in a 10" cast iron skillet so that they are all touching. 

Place the cast iron skillet in the oven and bake for 18-20 minutes. As soon as the biscuits come out of the oven, brush the tops with melted butter.