Pre-heat the oven to 425℉/210℃. Line a large baking tray.
In a bowl, combine the flour, baking powder, baking soda and salt and stir to combine.
Add the butter and rub into the flour using your fingertips (alternatively, do this in a food processor) until the butter is pea-sized and well blended.
Working fairly quickly, add the buttermilk, cheese, cooked bacon and jalapeño and stir with a metal spoon until just combined.
Tip this mixture onto a floured surface. Press down into a rectangle about 1 inch thick. Fold one side into the center, then the other side on top. Rotate the dough 90° and repeat x2.
Roll to about ¾ inch thick and cut out biscuits using a 3 inch cookie cutter. Make sure not to twist the cutter when using - simply stamp in and out.
Put the scraps back together and repeat until you have about 9 biscuits.
Place the biscuits on the lined baking tray. Place them close together so the sides are just touching. This makes the biscuits rise upwards rather than outwards. Brush the tops with any extra buttermilk. Bake 18-20 minutes until a strong golden color on top.
Remove, brush with a little melted butter and let cool slightly before serving.