Preheat the oven to 425°F and location a rack within the lower third of the oven. In a large shallow bowl, hurry the flour, baking powder, baking soda, and kosher salt. Add the chilled butter and employ a pastry blender or 2 knives to gash the butter into the flour till it is some distance the scale of peas. Dawdle within the buttermilk moral till the dough is moistened. Calmly dirt a piece surface with flour. Turn the dough out onto the outside and knead 2 or 3 cases, moral till it comes together. Pat the dough into a 1/2-prance-thick disk.
Using a floured 2 1/4-prance spherical cookie cutter, model out biscuit rounds as closely together as that you just’d mediate of. Accumulate the scraps and knead them together 2 or 3 cases, then flatten the dough and model out more biscuit rounds. Pat the last scraps together and gently press them into a biscuit.
Transfer the biscuits to a large baking sheet and brush the tops with the melted butter. Calmly sprinkle the biscuits with about a grains of flaky salt and take a seat again till firm, about 10 minutes.
Bake the biscuits for 20 minutes, or till golden. Let the biscuits frosty a diminutive bit of on the baking sheet sooner than serving.
The unbaked biscuits will seemingly be frozen: Freeze biscuits in a single layer and switch to a resealable plastic discover for as a lot as one month. Bake straight from the freezer, including a short time to the cooking time.