Cod With Artichokes And Chickpeas

Name: Cod With Artichokes And Chickpeas
Ingredients: 2 tablespoons unsalted butter; 1/4 cup extra-virgin olive oil; 1 small white onion, sliced 1/2 inch thick; One 9-ounce box frozen artichoke hearts, thawed and pressed dry; 1/4 pound shiitake mushrooms, stems discarded and caps quartered; 2 carrots, cut into 1/2-inch pieces; 2 garlic cloves, thinly sliced; One 15-ounce can chickpeas, drained; 1 cup chicken stock or low-sodium broth; Salt and freshly ground pepper; 2 tablespoons chopped flat-leaf parsley; 2 tablespoons snipped chives; Four 6-ounce skinless cod fillets; Lemon wedges, for serving