Carefully wash the potatoes. Without removing the skin, make deep incisions at various points but not all the way through. Cover the skin with a layer of extra virgin olive oil and season with salt and pepper.
After this, cover them completely in aluminium foil and place them on a very hot grill to cook for around 40 minutes.
In the meantime, cut the mortadella into slices, each around 2-3cm thick.
Once the potatoes are ready, sear the slices of mortadella on the grill for a few minutes.
Put the slices of mortadella on a plate along with the potatoes and decorate them with rosemary leaves.
To be served hot.