Step 1: Preheat your oven to 425°F (220°C) for perfect rising.
Step 2: In a large mixing bowl, whisk together the flour, sugar, baking powder, cream of tartar, and salt until well combined.
Step 3: Add the cold, cubed butter to the mixture. Cut in the butter until it resembles coarse crumbs.
Step 4: Fold in the cheddar cheese, jalapeño, and chives until evenly distributed.
Step 5: In a separate bowl, whisk together the buttermilk and egg. Pour this into the dry ingredients.
Step 6: Stir gently until the dough comes together, being careful not to overmix.
Step 7: Turn the dough onto a lightly floured surface, pat into a 1-inch thick rectangle, and cut out biscuits.
Step 8: Brush the tops with buttermilk and sprinkle with sea salt.
Step 9: Bake for 15-18 minutes until golden brown.
Step 10: Let cool for a few minutes, then enjoy warm!