Finely chop onions, garlic, spring onions, parsley, and sage leaves. 

Sauté everything in a pan with butter over medium heat. The onions should soften without browning.

Trim the pork tenderloin and cut a large pocket along the length of it.

Lay the ham slices side by side on a piece of cling film, ensuring the length matches the tenderloin.

Place the tenderloin on the ham, and fill the pocket in the tenderloin with the stuffing.

Roll the ham around the stuffed tenderloin and use the cling film to roll the tenderloin tightly. 

Let the tenderloin rest in the fridge until ready to cook, preferably for 30 minutes, but remember to take the meat out of the fridge at least 15 minutes before cooking.

Heat a frying pan well and carefully place the stuffed tenderloin in the pan, then reduce to medium heat. 

Cook the tenderloin for about 15 minutes on each side. 

Let it rest for a few minutes on a cutting board before slicing.

Personally, I like my pork tenderloin slightly pink.