Instructions

1. Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
2. On a lightly floured surface, roll out the puff pastry to a 12x12 inch square.
3. Spread the Dijon mustard evenly over the puff pastry, ensuring to cover it completely for maximum flavor.
4. Arrange the pastrami slices over the mustard, leaving a 1-inch border around the edges to ensure a good seal.
5. Layer the Swiss cheese over the pastrami, distributing it evenly.
6. Starting from one edge, carefully roll up the puff pastry like a jelly roll, making sure to keep the filling tightly packed.
7. Seal the edge of the roll with the beaten egg to prevent it from unraveling during baking.
8. Cut the roll into 1-inch slices and place them on the prepared baking sheet, spacing them apart to allow for expansion.
9. Brush the tops of the slices with the remaining beaten egg to achieve a beautiful golden color.
10. Bake for 20-25 minutes, or until the puff pastry is golden brown and flaky.