Mix cold unsalted butter, all-purpose flour, baking powder, and kosher salt together
Add diced jalapeños and grated cheddar cheese to the mixture
Add cold buttermilk (½ at a time) and mix until dough forms
Roll out dough on a floured surface and fold over on each other 4 times to create nice layers.
Cut into biscuit shapes
Brush with beaten egg and sprinkle with flaky sea salt (optional)
Bake at 375°F for 35 minutes until golden brown
