How to Make It
Fill a large pot with water, cover and bring to a boil. Add salt and the spaghetti. Cover partially until the water just returns to a boil, then uncover, stir the spaghetti and cook until al dente. Drain and transfer to a warmed large serving bowl, cover and keep warm.
Meanwhile, in a large skillet, heat 1/4 cup of the olive oil. Add the bread crumbs and cook over moderately high heat, stirring constantly, until golden and crisp, about 4 minutes. Transfer to a bowl and stir in the cheese.
Wipe out the skillet. Add the remaining 1/4 cup of olive oil, the sardines and the garlic and cook over moderate heat, stirring, until the sardines break up, about 2 minutes. Remove from the heat and stir in the dissolved tomato paste. Pour the sauce over the spaghetti and toss. Season with pepper and stir in 3 tablespoons of the bread crumbs. Sprinkle half of the remaining bread crumbs. Sprinkle half of the remaining bread crumbs on top and serve. Pass the remaining bread crumbs at the table.