Cut ½–inch slices off the tops of the onions.
Blanch the onions, by putting them into boiling water to cover and cooking for 30 minutes.
Drain and cool.
Scoop out the center of each, leaving about a ½ inch wall.
Combine the ground cooked meat with the chives, dried mixed herbs, and half the grated cheese.
Mash the egg yolk and chop the white; combine them with the rest of the mixture.
Stuff the onions with the mixture, mounding it slightly above the level of the onions.
Preheat the oven to 350°.
Place the onions in a greased roasting pan and sprinkle with the rest of the grated Gruyere cheese.
Bake for 30 minutes or until the cheese is lightly browned.
