Preheat the oven to 400°F (with the grill function).

Bring a pot of salted water to a boil. Cut the potatoes into large pieces and cook until tender.

Drain the cooked potatoes. Add the egg yolk, half of the butter, and a small splash of semi-skimmed milk. Season the mash with pepper, salt, and ground nutmeg. Mash everything into a creamy puree and set aside.

Trim the base of the chicory and remove any damaged leaves. Place the chicory in the pan with a splash of water. Bring to a boil.

Season the chicory with pepper, salt, and ground nutmeg. Cover with a circle of parchment paper and let it cook gently until lightly browned.

Drain the chicory well in a colander. Take each chicory stalk and roll it in a slice of ham.

In a saucepan, melt the other half of the butter. Add the flour and stir until you have a roux. Gradually pour in the semi-skimmed milk, stirring constantly.

Bring the sauce to a boil and add the grated Emmental cheese while continuing to stir, allowing the cheese to melt.

Season the cheese sauce with pepper, salt, ground nutmeg, and a spoonful of mustard. For extra flavor, add some of the chicory cooking liquid to the sauce.

Place the chicory rolls in a baking dish and spoon the cheese sauce over them.

Sprinkle some extra grated Emmental cheese over the cheese sauce. Place the baking dish in the preheated oven for 25 minutes to gratinate.

Serve the chicory rolls with the creamy mashed potatoes. Enjoy!