Heat the butter or olive oil in a large skillet over medium heat. Add the diced onion and cook, stirring occasionally, for 25-30 minutes, or until golden brown. Season with sea salt and freshly cracked pepper, to taste. Side Note: Add some water if the onion starts to get dry.
Add the minced garlic to the finished caramelized onions and cook, stirring constantly, for 1 minute.
When the onions are 10 minutes from being done, cook the pasta per the instructions in a large saucepan of well-salted water. Drain, reserving ¼ cup of the cooking water.
Add the drained pasta to the onion mixture along with the fresh parsley, and season with sea salt and freshly cracked pepper to taste. Add reserved pasta water, as needed.