In large bowl mix flour, baking powder, baking soda and salt.
Using a pastry cutter, cut in 10 Tbsp of butter. I like to use frozen butter and grate it into the flour mixture.
Stir in buttermilk until dough is moistened. DO NOT OVERMIX!
Turn dough onto floured surface, knead 2 to 3 times, until it holds together....again DO NOT OVERMIX. Pat down to about 1/2" thickness.
Using a biscuit cutter or top of a drinking glass, cut biscuit rounds as closely as possible. Place on buttered cookie sheet (I like to line it with parchment paper, no greasing necessary).
Gather scraps and press together to make more biscuits.
Once all biscuits are made, brush with remaining 2 Tbsp of melted butter.
Sprinkle with kosher or coarse salt.
Chill in freezer for 10 minutes
Bake for 20 minutes or until golden brown.
Notes
These biscuits can be frozen prior to baking. Frozen they are good up to 1 month. When you bake add a few minutes to baking time, do not thaw first.