Reserve the fennel tops, then cut the bulb into small cubes. Boil the cubes in a pot of salted water for 8 minutes. Add the raisins 1 minute before the end of cooking, then drain everything.
Squeeze the lemon juice. Pound the anchovy fillets in a mortar. Crush the rusks into fine breadcrumbs. Separate the sardines into fillets. Peel the garlic and crush it with a garlic press.
Drain the sardines, reserving their oil. Sauté the pine nuts in a pan with some of the reserved oil until browned, then add the garlic and anchovy paste, mixing well. Incorporate the fennel and raisins, mixing again.
When everything is sizzling, deglaze with lemon juice and reduce.
Cook the bucatini in a pot of salted boiling water according to the package instructions for al dente. Drain them.
Add the breadcrumbs to the mixture, season with pepper, and mix. Return the bucatini to the pot and add the mixture. Incorporate a bit more of the sardine oil and mix everything well.
Plate in 4 deep dishes, garnishing with sardine fillets. Add the fennel tops and serve.