1. In a large mixing bowl, combine the all-purpose flour, baking powder, sugar, salt, and a pinch of ground pepper.
2. Cut the butter into small cubes and add them to the dry ingredients in the bowl. Use your fingers to rub the butter into the flour mixture until it resembles breadcrumbs.
3. Stir in the grated cheddar cheese and chopped chives until evenly distributed.
4. In a separate small bowl, beat the egg lightly. If using Dijon mustard, add it to the beaten egg and mix until combined.
5. Make a well in the centre of the flour mixture and pour in the beaten egg mixture. Use a spoon or your hands to mix everything together until a dough forms. If the dough seems too dry, add a splash of milk until it reaches a soft dough consistency.
6. Flour a clean work surface lightly. Roll out the dough to about the thickness of your little finger.
7. Using a round cutter (about 6cm in diameter), cut out rounds of dough. Re-roll any trimmings to make more Welsh cakes.
8. Grease a flat griddle pan or heavy frying pan with butter or oil and place it over medium heat.
9. Cook the Welsh cakes in batches for about 3 minutes on each side or until they are golden brown and cooked through.
10. Once cooked, transfer the Welsh cakes to a wire rack to cool slightly.
11. Serve the savoury Welsh cakes warm, with butter, or enjoy them plain as a tasty snack or side dish.

These savoury, cheesy, herby Welsh cakes are perfect for any occasion. They can be enjoyed fresh or stored in an airtight container for later consumption. Enjoy!