Melt the butter in a pot and then add the onion, and cook until translucent.
Transfer the onion into a dish and set aside.
Add a tablespoon each of butter and oil to the pan and let them melt.
Add the potatoes, bell pepper, salt, pepper, and Italian seasoning, and stir together.
Cover and gently cook for 15 minutes and then add the sausage slices.
Cook for 10 minutes and then add the onions back into the pan and cook 5 minutes.
Serve with shredded parmesan on top as a garnish, offering extra parmesan on the side.