1) In a large sauce pan, combine the wild rice, 1 litre of the stock and salt to taste. Bring to a boil over high heat. Reduce the heat to maintain a gentle simmer, cover, and cook until tender, about 60 minutes. Drain and transfer the rice to a large bowl.
2) In a medium saute pan, heat 15g of the butter over medium heat and add the sausage meat. Cook, breaking it up with a wooden spoon, until it loses its raw colour, about 10 minutes. Drain off excess fat, and stir the sausage meat with the rice.
3) In the same pan, heat 30g of the butter over medium-low heat, add the onions, and cook until golden, about 15 minutes. Add the thyme and cook 2 minutes more. Stir the onion mixture with the rice.
4) Preheat the oven to 180C/Gas 4.
5) Melt the remaining butter in the same pan, over medium heat, and add the mushrooms. Cook until wilted and lightly browned, about 10 minutes. Add to the rice. Add the parsley and remaining stock. Season the rice mixture with salt and pepper to taste.
5) Transfer the mixture to a 23 by 33cm casserole dish, cover with foil, and bake until heated through about 30 minutes.