Beat the eggs thoroughly and season with salt and black pepper.
Melt the butter over low heat and add the beaten eggs.
Cook over low heat, stirring slowly but constantly.
Once the egg mixture has thickened but not yet become solid, add the cream and stir thoroughly.
Continue stirring, until the eggs turn into a solid but smooth mass.
While the eggs are still quite wet, add the Gruyère and mix thoroughly. There should be no lumps of cheese in the eggs; the mixture should remain smooth and uniform.
Just before the eggs are done, add the mustard and herbs. Mix thoroughly.
Taste and add salt and pepper if necessary.
Serve with buttered toast.