Soak the lace fat in hot water, then drain it and open it on a cutting board. Cut the pork liver into 12 pieces. Mix in a small bowl bread crumbs, salt, pepper and fennel seeds.
Season generously every piece of pork liver with the flavoured breadcrumbs, then wrap it in lace fat.
Preheat oven to 190°C.
Make a skewer alternating a cube of stale Tuscan bread, a sage leaf and a piece of pork liver wrapped in lace fat. You will obtain four skewers.
Lay the skewers in a greased pan and roast them for about 35 minutes.