Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper or a silicone baking mat.
In a large bowl, whisk together the baking powder, buttermilk, sour cream, and unsalted butter until smooth and combined.
Add the bread flour, baking soda, and salt and mix until a dough forms.
Turn the dough out onto a lightly floured surface and knead a few times until it comes together.
Roll the dough out to about 1/2-inch (1 cm) thickness and cut into desired shapes using biscuit cutters.
Place the biscuits on the prepared baking sheet and brush the tops with melted butter.
Bake for 15-18 minutes or until golden brown and cooked through.