Gnocchi with Sausage & Leek Ragù

-oz. can whole peeled tomatoes (preferably San Marzano)

sweet Italian sausage (about 2 links)

extra-virgin olive oil

large leek (white and light-green parts only), trimmed, halved lengthwise, rinsed well, and cut crosswise into thin half-moon slices (about 1-1/2 cups)

chopped fresh flat-leaf parsley

chopped fresh thyme

chopped fresh marjoram

minced garlic (about 1 medium clove)

kosher salt; more to taste

Freshly ground black pepper

Kosher salt

recipe Potato Gnocchi

freshly grated Parmigiano-Reggiano (optional)