Place the raisins in a small bowl of water to soak.

In a small glass, stir the saffron into 2 tablespoons (30 milliliters) of room temperature water until it dissolves. Set the saffron water aside for later.

Bring a large pot of water to boil and salt it generously. Add the fennel fronds into the water and boil for 5 to 7 minutes—until the stalks are tender. Remove the fronds with a slotted spoon and finely chop them. Keep the water simmering for later.

Heat 2 tablespoons (30 milliliters) olive oil over medium/high heat in a small skillet. Add the bread crumbs and toast them, stirring frequently, until they begin to brown. Set aside for later.

Add 3 tablespoons (45 milliliters) olive oil into a large non-stick pan, along with the diced onion and anchovy fillets. Heat over medium/low heat, stirring frequently, until the anchovies dissolve into the oil.

Drain the raisins and add them into the sauce, along with the saffron water, pine nuts, and sardine fillets. Increase the heat to medium, bring the sauce to a simmer, then stir and cook the fish for 2 minutes.

Stir the chopped fennel into the sauce, along with a generous pinch of salt and fresh black pepper. Let the sauce simmer for 5 minutes. Taste the sauce and add salt if needed, then turn off the heat while the pasta cooks.

Bring the fennel water back to a boil and add the bucatini. Cook as directed, but for 2 to 3 minutes less than the recommended 'al dente' cook time.

When the pasta is done, drain it with a spaghetti fork or tongs and transfer it into the sauce.

Continue to cook the pasta in the sauce over medium/high heat until the bucatini is al dente to your taste. If the sauce thickens too much, ladle in some of the pasta water as needed to maintain a simmer.

When the pasta nears completion, stop adding pasta water so that the sauce can thicken.

Serve immediately, topped with the toasted bread crumbs.