Preheat the oven to 200°C.
Drizzle some oil into the tin and put it into the oven to get hot.
Peel the onions and then cut them into 8.
Cut the potatoes into 8 (or 4 if small).
Cut the sausages into 4.
When the oven's ready, put the sausages, onions and potatoes in.
Sprinkle over salt and pepper to taste. Add some of the rosemary. Stir it all around to coat everything.
Put it in the oven for about 20 minutes.
When the time's almost up, peel the garlic cloves and cut them in half.
Peel the quince, cut into 8 and take out the core bits. (Easier than coring the quince first).
Take out the tin, and turn the oven down to 180 C. Throw in the garlic, quince and the rest of the rosemary.
Stir them around to coat, and to unstick anything from the tin.
Put it back in the oven for about 30-40 minutes until everything is done (check after 30 minutes).