Preheat oven to 450 degrees. Prepare baking sheet with parchment paper. Separate 4 Tbsp. butter, cut into ¼" dice, and put in refrigerator until use. Keep remaining butter out to soften. In a medium mixing bowl, combine 1 ¼ cup flour (reserve the rest for dusting on your workspace), white sugar, baking powder, half the cinnamon, baking soda, and 2 pinches of salt. Mix to combine. In a small bowl, mash sweet potatoes with a fork, add buttermilk, stir to combine, and set aside.