Rub the pork tenderloin well with salt and pepper. Briefly blanch the chard leaves and remove the thick stalks.
For the farce, cut the chicken fillet into large pieces, add the cream and spring onions and puree finely in the blender (you can also use a magic wand!). Then fold in the egg and herbs and season.
Place a large piece of aluminum foil on the worktop and put the same size cling film on it.
Spread out the chard leaves the size of the fillet on the foil, brush with the farce and place the pork fillet on top. Wrap with the two foils and press tightly (like a napkin ball).
Cook in gently simmering water for 30 minutes, remove and let simmer briefly in the 70 ° C oven. Unwrap carefully and cut open.
The meat is then still slightly pink and wonderfully tender.