Step 1

For the Toasted Breadcrumbs: If using fresh or lightly stale bread, adjust oven rack to middle position, and preheat oven to 325°F (165°C). (If using fully stale and dried bread, skip baking step.) Arrange bread in single layer on rimmed baking sheet, and bake until completely dried, 20 to 30 minutes. Remove from oven, and allow to cool to room temperature, about 5 minutes. Transfer oven-dried or fully stale bread to food processor bowl (set aside but don't clean rimmed baking sheet), and pulse until reduced to small crumbs, taking care not to over-process into a fine powder, 8 to 10 pulses.

Step 2

Combine breadcrumbs and 1 tablespoon (15ml) oil in a large skillet, and cook over medium-low heat, stirring and tossing occasionally, until crisp and golden brown, 8 to 10 minutes. Season lightly with salt. Transfer toasted breadcrumbs to reserved rimmed baking sheet, spread into an even layer, and set aside to cool to room temperature. Once cool, set aside 1/2 cup (60g) toasted breadcrumbs for the pasta, and transfer remaining crumbs to an airtight container for future use; the extra breadcrumbs can be stored at room temperature for up to 2 weeks.

Step 3

For the Pasta: In a large skillet, melt 3 ounces (6 tablespoons; 85g) butter over medium-low heat. Add anchovies and cook, stirring and breaking up anchovies occasionally with a rubber spatula or wooden spoon, until anchovies have dissolved, about 4 minutes. Reduce heat on skillet to lowest possible setting, to just keep warm while you boil the pasta; if your burner can only be reduced to a simmer, then turn heat off entirely.

Step 4

Meanwhile, in a large Dutch oven or wide-bottomed pot, combine 3 quarts (3L) of water and 2 teaspoons (8g) salt, and bring to a boil over high heat. Add pasta and cook, stirring frequently for first 30 seconds to prevent noodles from sticking.

Step 5

Once pasta has cooked for 5 minutes, transfer 1 cup (240ml) of pasta cooking water to skillet; continue cooking pasta. Return skillet to high heat and bring to a boil, swirling pan and stirring constantly until cooking water emulsifies with butter-anchovy mixture, 1 to 2 minutes. Reduce heat to low while pasta finishes cooking to prevent liquid from over-reducing.

Step 6

Meanwhile, continue cooking pasta until it is softened on the exterior, but well shy of al dente and still uncooked in the center (about 3 minutes less than the package directions). Using tongs, transfer pasta to skillet, and reserve remaining pasta cooking water. Alternatively, drain pasta using a colander or fine-mesh strainer, making sure to reserve at least 2 cups (475ml) pasta cooking water.

Step 7

Increase heat to high and cook, stirring and tossing rapidly, until pasta is al dente and sauce is slightly thickened and coats noodles with a creamy glaze, 2 to 3 minutes, adding more pasta cooking water in 1/4 cup (60ml) increments as needed. At this point, the sauce should be emulsified and loose enough to pool around the edges of the pan.

Step 8

Remove from heat, add remaining 2 tablespoons (30g) butter, lemon juice, and zest. Toss and stir rapidly to incorporate and emulsify butter into the sauce. Season with salt and pepper to taste. Divide between individual serving bowls, sprinkle with breadcrumbs and parsley, and serve.