1/ 2 cup walnuts, finely chopped but not pulverized (60 g)
2 / 3 cup freshly grated Parmesan cheese (70 g)
In a large pot of boiling salted water, cook the spaghetti until it is al dente.
While the pasta cooks, prepare the sauce: Rinse the arugula well and trim off the tough stems. Set aside a few leaves for garnish. Chop the remainder coarsely.
In a large skillet, heat the butter and olive oil over moderate heat. Add the arugula and cook, tossing, until it is wilted, 2 to 3 minutes. Pour in the cream, bring to a simmer, and cook for 2 to 3 minutes longer. Season with salt and pepper to taste. Stir in the chopped walnuts.
Drain the pasta well and add to the pan with the hot arugula. Toss over low heat, sprinkling on the cheese as you turn the pasta. Pour the pasta into a warmed serving dish and top with a grinding of black pepper. Garnish with the reserved arugula and serve at once.