Makes 10 biscuits

2 cups bleached all-purpose flour
2 teaspoons baking powder
1/4 teaspoon baking soda
3/4  teaspoon salt
1 cup grated extra-sharp cheddar cheese
1/4 cup thinly sliced scallion greens
1 stick (8 tablespoons) unsalted butter, frozen solid
1 cup cold buttermilk, a few extra teaspoons if necessary

Adjust oven rack to lower-middle position and heat oven to 450 degrees.  Mix flour, baking powder, baking soda, and salt with a fork in a medium bowl. Using a box grater, coarsely grate frozen butter into the dry ingredients; rub quickly with fingertips to evenly blend. Add cheddar and scallions; toss to coat With a fork mix buttermilk into dry ingredients until dough just comes together.

Pinch dough into 10 rough rounds, placing them on a small silpat-lined or vegetable cooking spray coated cookie sheet. Bake until golden brown, 15 to 18 minutes. Serve.