Prepare the sardines: Remove the heads, butterfly the sardines along the belly, and remove the backbones. Dredge half of the prepared sardines in flour and fry them in hot oil until golden. Remove, drain on paper towels, and set aside.
Make the sardine and saffron sauce: In a skillet, heat two tablespoons of olive oil with the garlic clove. Add the remaining (unfried) sardines and pour in half a glass of water. Cook for about 10 minutes. Dissolve the saffron in a couple of tablespoons of warm water and add it to the pan along with chopped parsley, salt, and pepper. Stir continuously so the sardines break down into a sauce. Cook for an additional 5 to 10 minutes, then remove from heat and set aside.
Prepare the onion, raisin, and pine nut mixture: In another pan, stew the chopped onion with half a glass of water and three tablespoons of olive oil. Add the raisins (previously soaked in water and squeezed dry), the pine nuts, the anchovy fillets, and finely chopped wild fennel. Cook over medium-low heat for about 10 minutes until the anchovies have melted and the flavors meld.
Cook the pasta: Meanwhile, boil the wild fennel seeds in a large pot of salted water for 15 minutes after reaching a boil. Remove the seeds with a slotted spoon, then cook the bucatini in the same flavored water until al dente. Drain the pasta and transfer it directly to the pan with the saffron sardine sauce. Drizzle with a little olive oil and toss thoroughly to coat.
Assemble: In an ovenproof baking dish, arrange alternating layers of the dressed pasta, the fried sardines, and the onion-raisin-pine nut sauce. Finish with a sprinkle of chopped fresh parsley and additional chopped wild fennel, if desired.
Bake and serve: Bake in a preheated oven at 180°C (350°F) for 15 minutes. Remove from the oven, let it rest for a few minutes to settle, and serve warm.
