01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - On a lightly floured surface, unroll or roll out the puff pastry into a rectangle approximately 10 x 12 inches.
03 - Evenly spread the Dijon mustard over the pastry, leaving a ½ inch border on one long edge.
04 - Arrange the ham slices over the mustard, then sprinkle with cheddar cheese and chopped herbs. Season with a pinch of black pepper.
05 - Starting from the long edge opposite the border, tightly roll the pastry into a log. Seal the edge with a small amount of water.
06 - Wrap the log in plastic wrap and place in the freezer for 10 minutes to firm up. This step ensures clean, even slices.
07 - Whisk together the egg and milk or water until well combined to create the egg wash.
08 - Cut the chilled log into ½ inch thick pinwheels, yielding approximately 24 pieces. Arrange them cut-side up on the prepared baking sheet, leaving slight space between each.
09 - Lightly brush the tops of each pinwheel with the egg wash mixture.
10 - Bake for 16 to 18 minutes, or until the pastry is fully puffed and golden brown.
11 - Transfer the pinwheels to a wire rack to cool for 5 minutes before serving warm or at room temperature.