Preheat the oven to 425 degrees F and line a baking sheet with parchment paper.

In a large bowl, whisk together the flour, baking powder, baking soda, salt, and sugar.

Cut the cold butter into the flour using a pastry cutter or your fingers, until the mixture looks like coarse crumbs with a few pea-sized pieces remaining.

Stir in the shredded cheddar and diced jalapenos until evenly distributed.

Pour in the buttermilk and stir just until the dough comes together, adding a splash more if it seems dry.

Turn the dough onto a lightly floured surface and pat it into a rectangle about 1 inch thick.

Fold the dough over itself two to three times to build layers, then pat it back down to about 1 inch thick.

Cut out biscuits with a round cutter, or slice into squares with a knife.

Place biscuits on the prepared baking sheet, close together for soft sides or spaced apart for crisp edges.

Bake for 15 to 18 minutes, until golden brown on top and cooked through. Serve warm.