Heat the butter and olive oil in a large pot over medium heat.
Add the onion with a sprinkle of salt and cook until softened, careful not to let it brown.
Add sausage, break it into smaller pieces, and cook until the meat is no longer pink.
Add garlic, oregano, and red pepper flakes, and cook until the garlic is fragrant, about a minute or two.
Stir in tomato paste and cook for a couple minutes more.
Add in the diced tomatoes and stocks.
Bring just to a boil, then reduce heat to a simmer and cook for about 20-30 minutes.
Raise the heat to a gentle boil and break the pasta into pieces and add to the soup. Cook until al dente.
Ladle soup into bowls and top with a scoop of the ricotta mixture.
If the soup isn’t served right away, then wait to add the pasta until ready to serve.