Whole roasted fish dishes like this flavorful one are traditionally served on Italian-American feast days.
½ cup plus 2 tbsp. olive oil
3 lb. yellow onions, sliced
3 lb. fennel, sliced, fronds reserved
¼ cup white wine
3 tbsp. finely chopped thyme
Zest and juice of 1 orange
Kosher salt and freshly ground black pepper, to taste
6 (2-lb.) whole branzino, cleaned
Heat oven to 350°. Heat ½ cup oil in a 12″ skillet over medium-high heat. Add onions and fennel; cook until soft, 8–10 minutes. Add fronds, wine, thyme, and zest and juice; cook for 5 minutes. Season fish with salt and pepper; stuff cavity with ¼ cup fennel mixture; tie fish closed with kitchen twine. Put remaining fennel mixture in a roasting pan; top with fish. Drizzle with remaining oil; bake until cooked through, about 30 minutes.