Adjust oven rack to middle position and heat oven to 450°F. Line a sheet pan with parchment paper or spray a sheet pan with cooking spray.
Measure 1 cup of buttermilk and place cup in the freezer while prepping other ingredients (you want it to be in the freezer about 10 minutes.
Place butter in a microwave safe bowl, cover with a paper towel and heat on high for 30 seconds. If not completely melted, return to microwave for 10 second intervals till melted. Set aside to cool a bit while prepping other ingredients.
Whisk flour, baking powder, baking soda, sugar, and salt in large bowl.
After buttermilk has been chilled in freezer for 10 minutes, combine it with 8 tablespoons of the melted butter. (Reserve the last tablespoon for brushing on the baked biscuits.) Stir with a fork until butter forms small clumps or globules.
Add buttermilk mixture to dry ingredients and stir with rubber spatula just until all flour is incorporated and batter pulls away from sides of bowl. Dough should be stiff and not super wet. If dough is wet, add more flour 1 tablespoons at a time, stirring to combine, until dough is fairly stiff.
Generously flour a work surface. Dump biscuit dough from bowl onto prepared work surface and turn to coat all surfaces with flour. Knead on counter 56 times (about 30 seconds). Flip over on work surface to coat with flour, then pat into a 6-inch square. It should be 1-½ to 2-inches in height. Cut four biscuits with a 2-½ inch biscuit cutter. Place biscuits on prepared sheet pan. Knead scraps a few times till they hold together, then pat into a small rectangle and cut two more biscuits. Transfer last two biscuits to sheet pan, spacing about 1-½ inches apart.
Place in oven and bake until tops are golden brown and crisp, 8 to 18 minutes. Start checking them after 8 minutes as ovens vary. You want them to be a nice golden brown but not too brown.
Remelt remaining tablespoon of butter in microwave, if necessary, and brush tops of hot biscuits with melted butter. Serve and enjoy!