Directions

1. Bring a large pot of water to a boil for the pasta.
2. In a large skillet, heat the olive oil, half a turn of the pan, over medium-high. Add the butter. When it foams, add the sausage and walnuts and cook, stirring and breaking up the sausage with the back of a spoon, until the sausage is cooked through and the mixture is deep golden brown, about 5 minutes.
3. Add the shallots and garlic and stir until the shallots soften, 1 to 2 minutes. Add the prosciutto and rosemary. Stir to heat through, 1 to 2 minutes. Add the brandy and stir, scraping up any browned bits on the bottom of the skillet. Add the cream and sage and bring to a bubble. Reduce the heat to low and let simmer, stirring occasionally, while the pasta cooks.
4. Salt the pasta water, add the pasta and cook until al dente. Drain, reserving half a mug of cooking water. Toss the pasta and 1 cup cheese into the sauce, adding cooking water as needed to thin the sauce. Serve in shallow bowls, passing more cheese alongside.