Set oven to 400°F/200°C, combination steam setting. If you have variable steam settings, use 50% (if you can’t vary your steam, don't worry! Just set to combi steam at the correct temperature and the oven will take care of the humidity). Line a baking sheet with parchment paper and set aside.
Mix the mustard and honey together until smooth and set aside.
2 Tablespoons dijon mustard, 1 teaspoon honey
Cut each pastry sheet into four squares. Divide the honey mustard mixture between the squares and spread out, leaving two diagonally opposite corners without the mustard mix. You’ll fold these corners over later to enclose your filling, so they need to be able to stick together.
2 Tablespoons dijon mustard, 2 sheets puff pastry, 1 teaspoon honey
Using half a piece of ham for each pastry (you may need to cut or fold to fit), lay it over the squares so it covers the centre but leaves the two bare corners empty.
4 slices leg ham
Lay 3 asparagus spears per pastry over the ham, then place a slice of cheese on top of the asparagus and season with ground black pepper. Bring up the two opposite corners of each pastry and overlap them to enclose the filling. You should have a little cheese and the ends of the asparagus poking out at the other corners.
24 asparagus spears, black pepper, 8 slices Swiss cheese
Place the pastries on the prepared baking sheet and brush the top of each one with a little beaten egg yolk.
1 egg yolk
Cook until puffed and golden all over, about 18 minutes. Serve warm.