Mix the dry ingredients:

1. In a large bowl, whisk together the flour, salt, and pepper. Add the chopped scallions and chives and toss to combine. Add the grated cheddar and toss again, making sure the cheese is evenly distributed and coated in flour — this prevents it from clumping.

Cut in the butter:

1. Add the frozen grated butter to the flour mixture. Using your fingertips, quickly snap and press the butter into the flour until the mixture looks like coarse, uneven crumbs with some pea-sized butter pieces still visible. Work fast — you want the butter to stay as cold as possible. If your hands are warm, rinse them in cold water first.

Form the dough:

1. Drizzle in 1 tablespoon of milk and stir gently with a fork. The dough should just barely come together — it will look shaggy and rough, and that is exactly right. If it is too dry to hold together when you squeeze a handful, add the second tablespoon of milk. Do not overmix.
2. Turn the dough out onto a lightly floured surface. Pat it into a rectangle about 1 inch thick. Fold it in half over itself, rotate 90 degrees, and pat it out again. Repeat this fold 3-4 times — this creates the flaky layers. Pat the final dough to about 1 inch thick.

Cut and bake:

1. Preheat the oven to 425°F. Line a baking sheet with parchment paper. Using a sharp biscuit cutter or a glass dipped in flour, cut straight down through the dough without twisting — twisting seals the edges and prevents the biscuits from rising tall. Place the biscuits on the baking sheet with their sides touching (this helps them rise higher). Sprinkle the tops with a pinch of flaky salt.
2. Bake for 15-18 minutes, until the tops are deeply golden brown and the biscuits have risen tall with visible layers on the sides. They should feel firm on top but still give slightly when you press them. Let cool for 5 minutes — if you break one open, you should see steam rising and layers pulling apart.