Chill your cubed butter in the freezer for 10-20 minutes before beginning this recipe. (It is ideal that the butter is very cold for light, flaky, buttery biscuits.)
Preheat oven to 400F and line a cookie sheet with parchment paper. Set aside.
Combine flour, baking powder, sugar, and salt in a large bowl and mix well. Set aside.
Remove your butter from the freezer, add to the flour mixture and stir with a wooden spoon or spatula. Mix the butter until the mixture resembles coarse crumbs.
Add buttermilk and stir until combined.
Add 1 cup of cheese and 2 tablespoons jalapeños, mix in to combine evenly. (Do not over work the dough. It will appear very crumbly at this point.)
Transfer your biscuit dough to a well-floured surface and use your hands to gently work the dough together. (If the dough is too sticky, add flour until it is manageable.)
Once the dough has come together, begin folding it in half, over itself and use your hands to gently flatten layers together. Rotate the dough 90 degrees and fold in half again. Repeat this step 5-6 times. (Take care to not overwork the dough.)
Use your hands (do not use a rolling pin) to flatten the dough to 1" thick.
Lightly dust a 2 ¾" round biscuit cutter with flour.
Making close cuts, press the biscuit cutter straight down into the dough and drop the biscuit onto your prepared baking sheet. (Repeat until you have gotten as many biscuits as possible.)
Gently re-work the cut scraps of the dough to get another biscuit or two until you have at least 6 biscuits.
Ensure the biscuits are placed less than ½" apart on the baking sheet, then brush lightly with 2-3 tablespoons buttermilk and add a jalapeño slice to each biscuit.
Bake on the middle rack of the oven for 20 minutes (until tops are beginning to just turn lightly golden brown.)
Remove baking sheet from the oven and brush with melted butter, sprinkle lightly with ¼ cup of cheese, then return to the oven for 3 minutes until cheese is melted.
Remove from oven, serve warm and enjoy.