1. Preheat the oven to 180°C (350°F).
2. Prepare the stuffing by mixing the sausage meat, ground beef, garlic, parsley, egg, and a little salt and pepper to taste.
3. Peel the potatoes and cut off a "lid" on the top. Hollow out the potatoes using a knife or spoon; keep the removed potato flesh. Fill the potatoes with the stuffing and place the "lids" on top of each potato.
4. Slice the onion. Butter an ovenproof dish, place the sliced onion at the bottom, then place the stuffed potatoes. Place the remaining potato flesh and any leftover stuffing in the dish. Place a knob of butter on each potato "lid" and pour the glass of broth over everything.
5. Bake for 55 minutes. Extend the cooking time by a few minutes if necessary.