Pre heat the oven to 160C fan forced.
Heat 2 teaspoons oil in a flameproof casserole dish (see tip) over medium heat. Add the sausages, cook turning until golden. Remove to a plate. Add remaining oil with the parsley stalks, garlic and onion. Saute, 5 minutes until softened. Add the stock, rosemary, sweet potato, pumpkin and carrots. Bring to the simmer. Return the sausages.
Cover with a lid (see tip). Place into the oven, cook for 30 minutes or until vegetables are almost tender.
Add the mushrooms. Return to the oven and cook for a further 20 minutes before removing from the heat.
Carefully transfer the liquid from the casserole dish into a saucepan. Bring to the boil over high heat, boil 5-8 minutes or until sauce has reduced and thickened .Pour the sauce back over the casserole, season and scatter with parsley.