Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.
Roll puff pastry into a rectangle on a lightly floured surface.
Spread Dijon mustard evenly over the pastry, if using.
Layer ham slices across the pastry, then sprinkle cheddar evenly on top.
Starting from the long edge, roll tightly into a log.
Slice into 1-inch rounds and place cut-side up on the baking sheet.
Brush tops lightly with beaten egg.
Bake for 15–18 minutes, or until golden brown and puffed.
Let cool slightly before serving.