Preheat your oven to 425 deg F. Line a dark baking tray with parchment paper. Alternatively, you can butter a cast iron skillet. Set it aside.
Place flour in a mixing bowl. Add cold and cubed butter to the bowl. Cut and mix butter into flour using a pastry cutter/fork. Combine till coarse crumbs form.
Add salt, baking powder, sugar, garlic, chopped jalapenos and 1/2 cup of cold buttermilk. Mix them in with light hands using a spatula/folding spoon.
Now add cheese and mix it in too. Do not over work the dough. It will appear very crumbly at this point!
Turn the dough out on a floured surface and form a rectangle out of the dough.
Now fold and flatten your dough a few times. Please check process pictures for reference. Then using your hands/rolling pin form a rectangle about 1/2-3/4 inch thick.
Cut into biscuits using a glass/biscuit cutter about 2-3 inches in diameter. Work with scraps till you have 5-6 biscuits.
Place on prepared tray/cast iron, top each biscuit with a sliced jalapeno and brush with remaining buttermilk. Bake for 15-17 minutes or until they appear golden brown on top.
Take the cheddar cheese biscuits out from oven and brush with melted butter generously. Enjoy warm!