Preheat your oven to 400°F (200°C). Line a baking tray with parchment paper or butter a cast iron skillet and set aside.
In a mixing bowl, combine the flour and cold, cubed butter. Use a pastry cutter or fork to cut and mix the butter into the flour until coarse crumbs form.
Add the salt, baking powder, sugar, garlic powder, chopped jalapenos, and 1/2 cup of cold buttermilk to the bowl. Gently mix them in with a spatula or folding spoon.
Add the shredded cheddar cheese and mix until just combined. Avoid overworking the dough; it may appear crumbly at this point.
Turn the dough out onto a floured surface and form it into a rectangle. Fold and flatten the dough a few times, then shape it into a rectangle about 1/2 to 3/4 inch thick using your hands or a rolling pin.
Cut the dough into biscuits using a glass or biscuit cutter about 2-3 inches in diameter. Gather and re-roll any scraps to make more biscuits.
Place the biscuits on the prepared baking tray or cast iron skillet. Top each biscuit with a sliced jalapeno, if desired. Transfer the tray to the freezer and freeze the biscuits for 10-15 minutes.
After freezing, brush the biscuits with the remaining buttermilk. Bake for 20-23 minutes or until golden brown on top.
Once baked, remove the biscuits from the oven and brush them generously with melted butter. Serve warm and revel in the deliciousness of these jalapeno cheddar biscuits!