Preheat oven to 450F.
Whisk flours in large mixing bowl. Grate frozen butter into flours and mix with hands until well distributed. Whisk in baking powder, soda, sugar, salt and pepper. Add chopped scallions to buttermilk and then to flour mixture. Gently incorporate wet into dry ingredients. When a dough has been achieved, turn out onto floured board and gently form into a rough square about 1 inch thick and cut into 8-10 squares (this is an estimate - you can make them whatever size you want to). Place on cookie sheet and brush with melted butter, sprinkle with coarse sea salt and black pepper and bake for 10-12 minutes, or until lightly brown on the top.