Preheat the oven to 375°F. Line a sheet pan with parchment paper and set aside.
Unroll crescent dough on your workspace. Separate into 4 rectangles (2 triangles press together) and pinch the seams together to form a rectangle.
Spread a thin layer of Dijon over each dough piece.
Layer one slice each of ham, turkey, then Swiss in even layers.
Starting from the long side, roll tightly into a log. Use a knife to cut each roll into 5 slices. Arrange cut-side up on the prepared sheet, spacing them slightly apart.
In a small bowl, whisk together the egg and water to form an egg wash. Brush the tops lightly with egg wash.
Bake for 12 to 15 minutes until puffed, golden, and the cheese is melted. Immediately remove from the pan and place on a serving dish. Dust lightly with powdered sugar and serve with jam!
Notes
Air fryer method: Cook at 350°F for 7 to 9 minutes, working in batches to avoid overcrowding.
Make-ahead: assemble the log in the morning, wrap, chill up to 24 hours, then slice and bake.
Storage: Keep leftovers in the fridge for up to 3 days. Reheat at 325°F for 6 to 8 minutes or in the air fryer at 320°F for 3 to 5 minutes.