Kosher salt and freshly ground pepper
1⁄2 lb (500 g) jumbo shells
2 teaspoon olive oil, plus more for greasing
5 oz (155 g) arugula leaves, tough stems removed
3 cups (24 oz/750 g) whole-milk ricotta cheese
6 tablespoons (1 1⁄2 oz / 45 g) freshly grated Parmesan cheese
1 large egg, lightly beaten
1 1⁄2 cups (12 fl oz / 375 ml) Amatriciana Sauce (see below)
2 tablespoons olive oil
4 oz (125 g) guanciale, pancetta, or unsmoked bacon, chopped
1 small yellow onion, chopped 
1⁄2 teaspoon crushed red pepper flakes
3 cloves garlic, minced
Kosher salt and freshly ground pepper 1 can (28 oz / 875 g) crushed tomatoes
1⁄2 teaspoon dried oregano