1) Preheat oven to 220C/Gas 8.
2) Combine flour, baking powder, bicarbonate of soda and salt in the bowl of a food processor. Pulse twice to distribute the ingredients evenly. Scatter the butter over the top of the flour mixture and pulse 4 or 5 times or until the mixture resembles coarse meal. Add the buttermilk and pulse until the mixture just begins to come together.
3) Scrape the dough onto a lightly floured counter. Pat the dough into a 25 by 30cm rectangle about 2cm thick. Use a 7 1/2cm round cutter to make 8 biscuits then place them on the prepared baking sheet. Press together the scraps of dough, and repeat process. Place the biscuits on 2 baking sheets lined with parchment paper; brush the tops with cream and sprinkle with black pepper. Bake the biscuits for 12 to 15 mins or until lightly golden brown. Remove from the oven and brush the tops with melted butter.