01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - Unroll the puff pastry on a lightly floured surface. If using, spread Dijon mustard evenly over the surface.
03 - Arrange ham slices evenly on top of the pastry, leaving a ½ inch border along one long edge. Sprinkle shredded cheese and chives (if using) evenly over the ham. Season with black pepper.
04 - Starting from the opposite long edge, tightly roll the pastry into a log toward the border. Press the edge to seal.
05 - Slice the roll into 16 even pieces. Place pinwheels cut side up on the prepared baking sheet, spacing them apart.
06 - Brush tops with beaten egg for a glossy finish.
07 - Bake for 15 to 18 minutes, or until golden brown and puffed.
08 - Let cool slightly before serving warm.