Remove the sausage from the casings, and form into small meatballs. In a skillet, add a tablespoon of olive oil and fry the meatballs until browned, crisp, and cooked through. Remove the meatballs with a slotted spoon and set aside on a plate.
Bring a pot of salted water to a boil for the pasta and cook according to package instructions, undercooking the pasta by 1-2 minutes. Drain, reserving about a cup of the cooking liquid.
Meanwhile, add another tablespoon olive oil to the skillet and add the sage. Once the sage is crisp, remove from the pan and set aside on a plate. Add 2 tablespoons butter to the skillet and cook the mushrooms until caramelized, along with the fresh thyme. Add the garlic and salt and pepper to taste. Cook for 3 minutes.
Add the half and half, along with the pasta, meatballs, and parsley. If the sauce needs to be loosened up a bit, add a bit of the reserved pasta water until you reach the desired consistency. Transfer to a serving bowl and top with the crispy sage, walnuts, and cheese. Serve!