In a large pot over medium heat, add butter, olive oil, and onion.

Cook onions, stirring every few minutes for 20-25 minutes, or until onions become golden brown (caramelize). Turn heat off and set aside.

When onions are about halfway done caramelizing, use a knife to remove sausage meat from casings.

Cook sausage meat in a separate dry pot over medium-high heat for about 10 minutes, until sausage is completely cooked through. Use a potato masher and/or large spoon to break up sausage into small crumbles as it cooks.

Cook pasta according to box instructions, or until al dente.

Add drained pasta and crumbled sausage to caramelized onion pot over low heat, tossing until combined.

Add a handful of chopped parsley, a large handful of parmigiano, a drizzle of olive oil if dry, and salt and pepper to taste.