Heat remaining 4 tablespoons oil in a large sauté pan on low. Add fennel and onion, and cook until soft but not brown. Add sausage and cook, mashing it to a fine crumble, until it is no longer pink. Add chicken stock and cook until the stock has mostly evaporated and just glazes the sausage. Transfer sausage mixture to a food processor and pulse until finely ground. Return sausage to the pan. Fold in broccoli rabe pesto. Set aside.
03Bring large pot of salted water to a boil. Add orecchiette and cook until al dente, about 7 minutes. Reheat sausage mixture and add about ½ cup of the pasta water. Drain pasta and add to pan with the sausage mixture. Toss ingredients together until pasta is evenly coated. Fold in remaining ½ cup cheese, check seasoning and serve.