Preheat oven to 450•
Combine flours, baking powder, baking soda, 1 tsp.salt, and sour cream in large mixing bowl.
With a cheese grater, quickly grate the frozen butter into the flour mixture.
Using a pastry blender (or fork) cut the butter into the flour mixture until it resembles a coarse meal.
Add the buttermilk a little at a time, stirring just until it clumps together and is no longer crumbly.
DO NOT overmix.
On a floured surface hand press the dough into a round 1" thick disk.
Using a round cookie cutter (or glass) cut into circles and place on a sheet pan (or in a cast iron skillet).
Bake for 15 minutes, or until slightly brown.
Brush with melted butter and lightly sprinkle with remaining salt.
Bake for another 5 minutes.
Yield depends on size of biscuits (approx 8).