Mix most of the cheese with the ham or gammon, egg yolks, mustard, herbs and some seasoning. Whisk egg whites until stiff. Using a rubber spatula, gently fold the whites into the yolk mixture until evenly mixed.
Heat a splash of olive oil in a small non-stick frying pan. Pour mixture into the pan and cook for 4 mins until the underside is set and browned. Sprinkle over the remaining cheese and grill for 2 mins until cheese is bubbling and golden.