Heat a large Dutch oven over medium high heat.
Add 2 tablespoons olive oil to the hot pan and heat an additional 30 seconds.
Add the sausage to the pan and cook, breaking it apart with the back of a wooden spoon until almost entirely cooked, 2 to 3 minutes.
Push the sausage to one side of the pan and add the mushrooms to the open spot. Season the mushrooms with ½ teaspoons salt and cook for 5 minutes.
Stir the mushrooms and cook an additional 3 to 4 minutes or until beginning to brown in spots.
Stir the mushrooms into the sausage and add the onion, carrots, celery, garlic and another ½ teaspoon salt. Cook, stirring often, until fragrant and the vegetables are beginning to soften, about 4 minutes.
Add the chicken broth, water, rosemary, parmesan rind, ¼ teaspoon salt and the rice. Stir to combine.
Bring to a simmer and reduce the heat to maintain a gentle simmer. Cover the pot and simmer for 35 minutes.
Uncover the pot and simmer until the rice is tender, an additional 30 minutes. If the stew gets too thick, stir in another ½ cup of water.
Remove the stew from the heat and stir in the remaining ¼ teaspoon salt and the mascarpone cheese.
Serve drizzled with olive oil and with a showering of freshly grated parmesan cheese.
