Adapted from A Common Table, by Cynthia Chen McTernan. This is truly a template. I describe three different techniques for making the dough, and list some potential ingredient substitutions in the recipe itself, but feel free to go further. I offer some additional ideas in the notes following the recipe.
In a large, wide mixing bowl, whisk together the flour, baking powder, baking soda, and salt.
If you have time, pop the bowl in the freezer for 5 minutes to chill.
Incorporate the butter into the flour mixture using one of the following methods:
If you are using fridge-cold butter, add the butter chunks to the flour mixture, and toss to combine. Then, either (1) cut the butter in using a pastry blender, until the butter is distributed and reduced to pea-sized pieces, OR (2) use your fingers to rub in the butter, flattening and smashing the chunks into thin discs or shards.
If you are using a stick of frozen butter, grate 6 tbsp of the frozen butter over the flour mixture using the large holes of a box grater. Using your fingers or a silicone spatula, gently toss the grated butter with the flour mixture to combine.
If you have time, return the bowl to the freezer for another five minutes while you gather the remaining ingredients.
Add the grated cheese and sliced scallions to the flour-butter mixture, gently tossing to distribute them.
Make a well in the center of the mixture and pour in about 3/4 cup of the cold buttermilk (or alternative). Using a silicone spatula, gently toss together the wet and dry ingredients until a shaggy dough starts to form. Once the liquid is mostly incorporated, use your hands to attempt to incorporate any lingering dry bits of flour, gently kneading the dough together. If the mixture is too dry to hold together, add a bit more buttermilk, no more than a tablespoon at a time--but be cautious. It's okay if the dough still seems a bit shaggy.
Turn the dough out onto a lightly floured surface and gently pat it or roll it into a rectangle about 1/2 inch thick. Using a bench scraper or bowl scraper to help you if necessary, fold the rectangle into thirds, like a business letter. Gently pat or roll the the dough back into a 1/2 inch thick rectangle, do another business letter fold, and pat the down into a 1-inch thick rectangle.
Transfer the rectangle of dough to a parchment-lined baking sheet, and place the sheet in the freezer for 10-15 minutes.
Meanwhile, preheat the oven to 425 F.
Remove the pan from the freezer, and transfer the dough rectangle to the counter or a large cutting board. To make round biscuits, use a 2.5-inch or 3-inch biscuit cutter to cut out as many biscuits as you can, pressing straight down. Pat together the scraps and repeat until you have used up all the dough. To make triangular or square-shaped biscuits, just use a bench scraper or sharp knife to cut the dough into 6 pieces.
Transfer the cut-out biscuits to a fresh parchment-lined baking sheet. Brush the tops with egg wash (made from egg that has been lightly beaten with a splash of water, milk, or cream), melted butter, heavy cream, or additional buttermilk.
Place the baking sheet in the oven and bake the biscuits for about 13-18 minutes, until risen and golden. (The baking time will vary depending on the size of your biscuits, how chilled your dough is, and whether your oven runs hot or cold.)
Remove from the oven, allow to cool on the baking sheet for a minute or two, and devour.