Heat the olive oil in a large pot over medium-high heat. Add the sausage, breaking it into small pieces as it cooks, for 5-7 minutes until browned and cooked through. Remove the sausage with a slotted spoon and set aside on a paper towel-lined plate. This step renders out the fat and develops deep flavor that will anchor the entire soup.
In the same pot with the rendered sausage fat, add the diced red bell pepper, sweet onion, and carrots. Sauté for 3-4 minutes until they begin to soften and release their natural sugars. Add the minced garlic in the final minute and stir constantly so it becomes fragrant without burning. I like to let the garlic just kiss the hot oil—this mellows its raw bite and builds a sweeter, more rounded base for the soup.
Stir in the oregano, basil, thyme, red pepper flakes, salt, and black pepper, mixing well to coat the vegetables and allow the dried herbs to bloom in the fat for about 30 seconds. Return the cooked sausage to the pot and stir to combine. Blooming the spices this way releases their essential oils and ensures even distribution throughout the soup rather than ending up in clumps.
Pour in the marinara sauce and chicken broth, stirring to combine. Add the parmesan rind to the pot—it will slowly dissolve and impart a salty, umami richness that deepens the overall flavor profile. Bring the soup to a simmer over medium heat. Break the lasagna sheets into 1-inch pieces and add them to the simmering broth, stirring occasionally to prevent sticking. Simmer for 14-15 minutes, until the pasta is tender but not mushy. I always use Rao's marinara because its clean tomato flavor lets all the spices and herbs shine through without competing.
Reduce heat to low and stir in the cream and mozzarella, allowing the cheese to fully melt and incorporate into the broth for about 1-2 minutes. The soup should now have a rich, slightly creamy consistency. Taste and adjust seasoning if needed, adding the sugar if you find the sauce tastes too acidic.
Ladle the hot soup into bowls and top each serving with a dollop of ricotta, a generous spoonful of basil pesto, freshly grated parmesan, and a few torn leaves of fresh basil. The cool ricotta and pesto contrast beautifully with the hot, spicy soup, creating layers of flavor and texture in every spoonful.