For the chard gratin, wash the chard well. Cut off the stems, chop into bite-sized pieces and bring to the boil in salted water, simmer for about 5 minutes and only then add the whole leaves and cook for another 2 minutes. Then drain in a colander and let cool.
Separate the eggs and whisk the yolks with the cheese, breadcrumbs and half of the soft herb butter. Beat the egg whites until stiff and fold them in, then add the chard mixture.
Line a baking dish with 1 tablespoon of the herb butter, pour in the mixture and top with the remaining herb butter. Bake the chard gratin, covered, in a 200 degree oven at top/bottom heat for about 35 minutes.