In a small saucepan, heat the butter over medium heat until it turns golden-brown, 2 to 3 minutes. Pour into a small bowl and set aside.
In a 12-inch skillet, heat the olive oil over medium-high heat. Add the tomatoes and cook until they start to blister, 2 to 3 minutes. Add the fennel and garlic. Cook, shaking the pan, until the garlic becomes golden-brown, 2 to 3 minutes. Add the escarole and stir for 1 minute. Add the sherry, raise the heat to high, and cook until it evaporates, about 30 seconds. Add the fish broth and boil until it reduces slightly, 3 to 4 minutes. Add the clams, cover, and cook for 2 minutes. Add the mussels, cover, and cook for 2 minutes. Add the shrimp, cover, and cook for 1 minute. With a slotted spoon, transfer the open shellfish and shrimp to a large bowl and cover loosely with foil. Toss any that do not open.
Stir the kale and pepper flakes into the broth and cook until the kale wilts, about 1 minute. Remove from the heat and add the parsley and rosemary. Pour in the browned butter. Add the lemon zest and juice. Season to taste with salt and pepper.
Distribute the broth, vegetables, and seafood among 4 wide, deep bowls. Garnish with parsley.
For an authentic Italian Feast of the Seven Fishes, start with two fried seafood hors d'oeuvres: salt-cod fritters and calamari rings before the mixed shellfish dish. Then for the main course, serve red snapper in a spicy puttanesca sauce paired with sautéed broccoli raab and a simple spaghetti with pecorino and garlic. A rich cannoli-inspired cheesecake, flecked with orange zest and chocolate chips, finishes the meal.
nutrition information (per serving):
16, Fat Calories
140, Saturated Fat
27, Monounsaturated Fat
10, Polyunsaturated Fat