1 teaspoon kosher salt, plus more for pasta pot
1 pound rigatoni
3 tablespoons extra-virgin olive oil
1 medium onion, chopped
1 pound sweet Italian sausage without fennel seeds, removed from casing
1 pound mixed fresh mushrooms
(button, cremini, shiitake, oyster), thickly sliced
6 fresh sage leaves
28-ounce can Italian plum tomatoes, preferably San Marzano,
crushed by hand
1 cup frozen peas
1 bunch scallions, chopped
1/2 cup heavy cream
1 cup grated Grana Padano or Parmigiano-Reggiano
Bring a large pot of salted water to boil for pasta. Slip the rigatoni into the pasta water, and cook until al dente.
Heat the olive oil in a large skillet over medium heat. Add the onion, and cook until softened, about 4 minutes. Add the sausage, and cook, crumbling with a wooden spoon, until the sausage is no longer pink, about 4 minutes.
Add the mushrooms, then cover, and cook until the mushrooms release their juices, about 2 minutes. Uncover, and add the sage and tomatoes. Bring to a simmer, slosh out the tomato can with 1 cup pasta water, and add it to the sauce, along with the salt. Bring the sauce to a simmer, and cook, uncovered, until thickened, about 10 minutes.
Once the sauce is thickened, toss in the peas and scallions. Cook until the scallions wilt, about 2 minutes. Pour 1 cup pasta water and the heavy cream into the sauce. Bring to a boil, and cook until thickened, about 2 minutes.
When it is cooked, remove the pasta with a spider and add directly to the sauce, tossing until the pasta is coated. Remove from heat, and sprinkle with the grated cheese. Toss again, and serve immediately.