Step 1

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.

Step 2

Melt 2 Tbsp. chilled unsalted butter by whatever method is easiest for you; set aside. Whisk 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, and 2½ cups (313 g) all-purpose flour in a large bowl to combine.

Step 3

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.

Step 4

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.

Step 5

Turn out onto a lightly floured surface and knead once or twice until it comes together; flour your hands if needed. If there are any loose bits, add them to center of dough and knead once more to incorporate.

Step 6

Pat dough into an 8x4” rectangle about 1” thick.

Step 7

Working from a short side, fold dough in thirds as you would a letter. It doesn’t need to overlap perfectly. Pat dough into another 8x4” rectangle, then fold dough in thirds like a letter one more time. (You'll have done the folding procedure two times total.) Pat dough back into an 8x4” rectangle and straighten up with your hands and/or your bench scraper. (This folding method is what will create those nice flaky layers in your final biscuits.)

Step 8

Cut rectangle in half lengthwise, then cut each half crosswise into 4 squares for a total of 8 biscuits.

Step 9

Transfer biscuits to prepared baking sheet. Brush tops gently with melted butter; sprinkle with flaky sea salt.

Step 10

Bake biscuits until golden brown, 18–22 minutes. Serve warm with sour cream (or more butter!) for slathering.