In a large bowl combine the flour, baking powder, baking soda, salt and 2 1/2 tbsp of the fresh dill. Stir with a fork to combine; set aside.
Using a box grater, grate the frozen butter. Add it to the flour mixture along with one cup of the grated cheese and gently use your hands to toss the flour and cheese around to coat the butter and cheese pieces (too much mixing will melt the butter).
In a small bowl, whisk together the egg, sour cream and buttermilk.
Make a well in the center of the flour mixture and add the egg mixture. Use a fork to mix and gradually form a sticky dough.
Lightly flour the counter top and dump the scone mixture out on top. With floured hands, knead the mixture about 10 times to form a shaggy, sticky dough.
Lightly flour the top of the dough and pat it into a rough circle 7 inches in diameter (I'm using an 8" skillet here). Use a scraper or long knife to score the circle into 8 even wedges (similar to cutting a pie) and still keep it in a circular shape.
Transfer the dough to a cast iron skillet. Bake for 18 minutes. Top with the remaining 1/2 cup of cheese and bake for 5 more minutes. As soon as the scones come out of the oven, sprinkle with the remaining 1/2 tbsp of dill. Serve immediately.