In a large pan (must be large enough to hold the entire dish), warm up 1/3 cup of the olive oil over medium heat, then sauté the onion and fennel. Cook for about 5 minutes, or until they just start to soften, and add garlic, salt, and pepper.
Cook until the onion and fennel are soft then add wine, stirring to combine. Add the anchovies, breaking them up with wooden spoon. Next, add sardines and, once they are heated through, add the raisins and pine nuts. Turn the heat down to low and continue cooking, making sure it doesn't burn.
Meanwhile, boil pasta until it is al dente. Drain the pasta, reserving some of the pasta water for later (or, you can simply pull the cooked bucatini out of the water and add directly to the sauce).
While pasta is cooking, place the pulsed bread crumbs into a hot skillet with the remaining oil and toast the breadcrumbs until they begin to brown. Season with a bit of salt and pepper and anything else you desire (some people add ground fennel); set aside
Add the drained pasta to the sardine mixture - adding some of the pasta cooking water will add a 'smoothness' to the sauce because it has some of the starch that leaches out of the pasta while cooking. Plate your pasta and sprinkle with the toasted breadcrumbs and drizzle with more olive oil and serve with reserved fennel fronds