How to Make It
In a small skillet, toast the fennel seeds over moderate heat until golden and fragrant, about 2 minutes. Transfer the fennel seeds to a plate.
In a large deep skillet, melt the butter in 1/4 cup of the olive oil. Add the garlic and cook over moderate heat until golden. Add the mushrooms, fennel seeds, rosemary and pepper and cook, stirring occasionally, until the mushrooms are tender, about 15 minutes.
Meanwhile, cook the pennette in a large pot of boiling salted water until al dente; drain. Add the pasta to the mushrooms along with the arugula, 1/4 cup of grated Pecorino and the 1 remaining tablespoon of olive oil. Mound on plates and serve with the extra Pecorino.