Pangrattato is simply fresh breadcrumbs with herbs, garlic and salt sautéed in hot olive oil until crunchy to top this quick-cooking pasta. We add pancetta and chopped walnuts for even more richness.
Bring a large pot of water to a boil. Cook pasta according to package directions. Reserve 1/2 cup of the water, then drain the pasta and return to the pot. Cover to keep warm.
Meanwhile, cook pancetta in a large skillet over medium heat until browned and crispy, 3 to 6 minutes. Transfer to a paper-towel-lined plate with a slotted spoon.
Add breadcrumbs to the pan and cook, stirring often, until starting to brown, 1 to 3 minutes. Add walnuts and cook, stirring occasionally, until toasted, 2 to 5 minutes. Add rosemary and half the garlic and stir to combine. Cook until fragrant, 30 to 60 seconds. Transfer the mixture to a small bowl and stir in the pancetta.
Add oil to the pan and heat over medium-high heat. Add leeks and cook, stirring often, until just starting to brown, 3 to 6 minutes. Add the remaining garlic and cook until fragrant, 30 to 60 seconds. Stir in wine and crushed red pepper; cook until the wine is almost evaporated, 30 to 60 seconds. Stir in tomatoes and the reserved 1/2 cup pasta-cooking water. Bring to a simmer. Add the pasta and toss to coat with the sauce. Cook, tossing the pasta with tongs, until the sauce thickens, about 1 minute. Add 1/2 cup of the pancetta mixture and toss to combine. Serve topped with the remaining pancetta mixture.
Tip: To make your own fresh breadcrumbs, trim crusts from whole-wheat bread. Tear the bread into pieces and pulse in a food processor until coarse crumbs form. One slice makes about 1/2 cup fresh breadcrumbs.