Preheat oven to 375 degrees F and bring a large pot of salted water to a boil.
Toss the mushrooms with 1 tablespoon of the oil, the chopped rosemary, 1 teaspoon salt and a few grinds of pepper. Arrange on a baking sheet in one layer and roast, stirring occasionally, until mostly dry and crisp in places, 40 to 50 minutes.
Meanwhile, heat the remaining tablespoon oil in a medium saucepan over medium-high heat. Add the sausage and garlic and cook, breaking up the clumps with a wooden spoon, until brown, about 6 minutes. Add the marinara, the rosemary sprig, and 1 cup water and bring to a simmer. Reduce the heat to medium and cook, stirring occasionally, until slightly thick, about 15 minutes. Season with salt and pepper.
Add the pasta to the boiling water and cook according to package directions. Drain and transfer to a large serving bowl and toss with the sausage sauce. Serve topped with the mushrooms and grated cheese.
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