Cook the onion, garlic and sausage in a 10-inch (25cm) skillet over medium heat, breaking up the meat and stirring often, until the sausage is browned with no pink remaining and reaches 160°F (71°C).
Drain off the excess fat.
Stir in 2 tablespoons of the parsley, the sugar, basil, diced tomatoes and tomato sauce.
Bring the mixture to a boil, stirring often. Reduce the heat and simmer uncovered for 45 minutes, stirring occasionally, until noticeably thicker.
While the sauce simmers, preheat the oven to 350°F (180°C). Cook the noodles according to the package directions, then drain them well.
Combine the ricotta with ¼ cup (25g) parmesan, the remaining 1 tablespoon parsley and the oregano. Divide the ricotta mixture in half.
Spread 1 cup (250ml) of the sausage sauce across the bottom of an ungreased 13×9-inch (33×23cm) glass baking dish.
Arrange 4 noodles over the sauce. Spread half the ricotta mixture over the noodles, followed by 1 cup (250ml) sausage sauce and ⅔ cup (75g) mozzarella.
Repeat with 4 noodles, the remaining ricotta mixture, 1 cup (250ml) sausage sauce and another ⅔ cup (75g) mozzarella.
Add the last 4 noodles. Spoon the remaining sausage sauce over them, then add the remaining ⅔ cup (about 75g) mozzarella and ¼ cup (25g) parmesan.
Cover the dish with aluminum foil and bake for 30 minutes. Remove the foil and bake for 15 minutes more, until hot and bubbling and the center reaches 165°F (74°C).
Rest the lasagna for 15 minutes before cutting it into 8 portions.
