We finished this quickly when my mom prepared it on those hectic evenings.

Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Roll out the puff pastry on a lightly floured surface to smooth out any creases.
In a small bowl, mix the beaten egg with the milk to create an egg wash.
Spread the Dijon mustard evenly over the pastry, leaving a small border around the edges.
Sprinkle the diced ham and shredded cheese over the mustard layer, then season with salt and pepper.
Carefully roll the pastry into a log, starting from one of the longer sides, and seal the edges with a bit of the egg wash.
Slice the log into 1-inch pieces and place them cut-side up on the prepared baking sheet.
Brush the tops with the remaining egg wash for a golden finish.
Bake in the preheated oven for 15-20 minutes, or until the pastries are puffed and golden brown.
Allow to cool slightly before serving.
Variations & Tips
For a touch of sweetness, you can add a spoonful of apricot preserves to the mustard layer. If you prefer a spicier kick, try adding a pinch of red pepper flakes or a dash of hot sauce to the filling. For a vegetarian version, replace the ham with sautéed mushrooms or spinach. You can also experiment with different cheeses, such as Swiss or mozzarella, to create your own unique flavor combination.