Line a large baking sheet with a silpat or parchment paper.
Whisk the flour, baking powder, salt, and black pepper together in a large bowl until well-mixed.
Use a pastry blender to work in the butter until the mixture is crumbly with pea-sized crumbs. Stir in almost all the cheese (leaving a little for sprinkling on top) and the chopped herbs.
In a separate bowl, whisk the egg, buttermilk, and mustard together. Reserve a tablespoon of the mixture to brush over the tops.
Make a well in the middle of the flour mix and pour in the buttermilk mixture. Stir until the mixture forms soft, spongy dough.
Turn out onto a lightly-floured surface and knead the dough briefly until smooth. Roll out to a 3-cm thick square. Cut into quarters, then cut each quarter diagonally to make 8 triangles.
Place the triangles on the prepared pan and brush the tops with the buttermilk mixture. Sprinkle with the remaining cheese.
Bake on convectional heat for 15 minutes or until the scones are well risen, golden, and sound hollow when tapped on the bottom. Good eaten warm, or at room temperature, or split and toasted with butter.