Melt your butter or oil in a large skillet over medium-low heat. Add the sliced onions and cook, stirring frequently, for about 25-30 minutes, until nicely caramelized.
Once your onions are golden brown, add garlic, bay leaves, thyme, wine, and broth. Bring to a heavy simmer, stir, then turn to a low simmer.
Add the beans and season with sea salt and pepper to your taste.
Allow your beans to simmer in the onion sauce for 10-12 minutes, to combine the flavors.
Stir in freshly grated parmesan cheese if desired and simmer for 2-3 minutes to thicken up the sauce.
Remove the bay leaves just before serving.
Serve with additional grated parmesan if desired and enjoy!