1. Preheat the oven to 350 degrees. Spread the walnuts on a rimmed baking sheet and toast until lightly golden and fragrant, about 8 minutes. Let cool.
2. Bring a large pot of water to a boil. Cook the linguine according to package directions. Drain, reserving 1/2 cup cooking water.
3. Combine the parsley, sage, garlic, salt, black pepper and walnuts in a blender; pulse until finely chopped. Drizzle in the olive oil and blend well. Add 3 tablespoons of the Parmesan; pulse quickly to combine.
4. Transfer the pesto to a serving bowl and add 1/3 cup cooking water. Add linguine and toss to combine, adding remaining pasta water as necessary. Top with remaining cheese and additional black pepper to taste.