Preheat oven to 450°F. Line a large sheet pan with parchment paper or foil and set aside.
In a mixing bowl, whisk together flour, baking powder, sugar, baking soda, and salt.
Toss cold butter cubes into the dry ingredients and, using a pastry cutter or your fingers, mix in the cold butter until you have a mixture of flat pieces and crumbly, pea sized bits of butter mixed into the flour.
Toss in your shredded cheese and finely diced jalapeño pepper.
Add the cold buttermilk and gently mix together with the dry ingredients until you have a loose dough. The flour won't look all mixed in and it will be crumbly, and that's okay. It will come together in the next steps.
Dump the dough mix out onto a lightly floured surface. Using your hands, gently bring everything together into a rough square.
With a bench scraper or knife, cut into four smaller squares. Stack the pieces of biscuit dough on top of each other. Press it all down into a square again. Repeat this cutting and stacking procedure 2 more times.
Pat or roll the dough into a rectangle about ½ to ¾ inch thick. Using a biscuit cutter or cookie cutter, cut out your biscuits. Gather your scraps as you go and gently re-form them together and cut as many biscuits as you can. If you have time, place sheet pan in the freezer for 10-15 minutes while you preheat your oven.
Remove biscuits from the freezer. Brush the tops of the biscuits lightly with an egg wash and sprinkle with flaky sea salt, if desired. Bake in a 450° oven for 18 to 20 minutes, or until golden brown.