Portion the fish fillet into six pieces of the same size, if possible. Salt carefully - the ham will make it salty anyway - and pepper on both sides. Each piece of fillet is covered with a sage leaf on the front and back and wrapped in a slice of ham. Carefully fix the saltimbocca with a toothpick.
Now melt the butter in a pan and fry the saltimbocca over medium heat for about 5 minutes until crispy. Cover and let rest for 10 minutes so that the fish can cook. Then serve.