Preheat oven to 400 degrees F.
Heat 1 tablespoon olive oil in a large Dutch oven or braiser over medium-high heat. Add onions and sauté for 5 minutes. Add the sausage and cook until sausage is cooked through and onions are softened. Add garlic and red pepper flakes and cook for 1 minute. Add the tomato paste and cook for 1 additional minute.
Stir in marinara, broth, all herbs and seasonings.
Bring to a boil, then add the broken lasagna noodles. Press down to submerge them in the liquid. Cover, and reduce to medium. Simmer until pasta is al dente, about 15 minutes (bendy and nearly tender but not fully cooked), stirring occasionally and replacing the lid so the noodles don’t stick and burn. Test for doneness early and cook on as needed.
Meanwhile, whisk the ricotta with sour cream, salt and pepper in a small bowl; set aside.
Reduce heat to low and stir in 1 cup mozzarella and 1/4 cup Parmesan until melted.
Remove from heat and sprinkle with remaining Parmesan. Dollop with ricotta mixture, then sprinkle with remaining mozzarella.
Bake, uncovered, at 400 degrees F, for about 8-10 minutes, until cheeses are melted. Let stand for 5 minutes before serving. Garnish with fresh basil and/or parsley if desired.