12 Tbsp. chilled unsalted butter, divided
2½ tsp. Diamond Crystal or 1½ tsp. Morton kosher salt
1 tsp. freshly ground black pepper
1¾ tsp. baking powder
½ tsp. baking soda
1¼ tsp. sugar
2½ cups (313 g) all-purpose flour, plus more for surface
1¼ cups sour cream, plus more for serving
Flaky sea salt
Place a rack in middle of oven; preheat to 425°. Line a baking sheet with parchment paper. Trim root ends from 8 scallions. Thinly slice crosswise (not on a diagonal); set aside.
Cut remaining 10 Tbsp. chilled unsalted butter into ½” pieces. Add to dry ingredients and toss to coat. Using your hands, work butter into dry ingredients, smashing it between your fingers and flattening it between your palm until there are lots of thin shards and pea-size bits. Add reserved scallions and toss to evenly distribute.
Create a well in the center of mixture and add 1¼ cups sour cream to the center. Using a fork and working in circles, mix until large shaggy clumps form. If your bowl is wide enough, fold dough over itself a couple of times inside it until it comes together.