Preheat oven to 425 degrees F (220 degrees C) and line a large baking tray with parchment.
In a large bowl whisk together All-Purpose Flour (1 1/2 cup), Cornmeal (1/2 cup), Granulated Sugar (2 tablespoon), Baking Powder (2 1/2 teaspoon), Kosher Salt (3/4 teaspoon) and Baking Soda (1/2 teaspoon).
Add Unsalted Butter (1/2 cup) and using a pastry cutter, cut butter into dry ingredients until pea-sized and evenly distributed.
In a separate bowl, whisk together Buttermilk (3/4 cup) and one Egg (1). Add mixture to dry ingredients and stir until just starting to come together.
Add Cheddar Cheese (1 1/2 cup) and Jalapeño Pepper Slices (1/4 cup) and continue to mix until just incorporated, being careful not to overmix. It will be a bit of a scraggly mess.
Flour your work surface and dump out the dough. Knead dough a few times to bring everything together. Flatten dough into a 3/4 to 1 inch disk. Using a 3-inch round cutter, cut out biscuits.
Reform remaining dough and cut out biscuits. Place biscuits on a parchment lined baking tray.
Whisk together Egg (1) and Milk (1 tablespoon). Brush biscuit top and sides generously with the mixture.
Bake for about 18 minutes, until golden and puffed.
Remove from oven and allow to rest on the tray for 3 to 5 minutes before moving to a cooling rack. Serve slightly warm. Enjoy!