2 pounds fennel bulbs, greens removed.
3 pounds whole fresh sardines
Semolina flour, for coating
2 medium onions, minced
1 teaspoon grated nutmeg
Salt and pepper, to taste
Boil the fennel in salted water until tender, about 20 minutes. Drain, reserving ¾ cup of the cooking liquid. Finely chop the fennel and set aside. Remove the heads of the sardines and pull out the backbones and entrails. Select several sardines for garnish. Season the sardines to taste with salt and pepper and coat them with the semolina flour. In a small saucepan, heat the ½ cup of olive oil over medium heat. When the oil begins to smoke, cook each flour-coated sardine until a light golden brown, about 1 minute on each side. Using a slotted spoon, remove the sardines from the pan and set them aside to drain on a paper towel.
In a 3-quart saucepan, heat the remaining oil over medium heat until shimmering. Add the minced onions and cook until soft and a light golden brown, about 8-10 minutes. Add the fennel, anchovies and nutmeg. Season to taste with salt and pepper. Bring the sauce briefly to a boil and then lower to a simmer. Add the remaining sardines and cook, stirring occasionally with a wooden spoon, until the sardines have broken into pieces and are thoroughly mixed into the sauce, about 10-15 minutes. If the sauce appears too thick at this point, add a little of the reserved fennel water.
Bring 6-quarts of water and two tablespoons of salt to a rolling boil. Add the spaghetti and cook until tender but still al dente. Drain the cooked pasta, and pour into the pan with the sardines and oil. Toss quickly over high heat until combined. Pour into 4 warmed pasta bowls and top with the fried sardines.