Heat the saucepan over medium-high heat and add the butter.
When the butter begins to bubble, add the ground beef and chopped onion.
Cook, stirring and breaking up the beef, until the beef is browned and the onion is soft, about 5 minutes.
Add the canned whole tomatoes and the Italian herb spice mix to the pan.
If using whole tomatoes, mash them in the pan with a potato masher or large ladle until broken up.
Bring to a simmer, then reduce the heat to low and let the sauce simmer gently for 45 minutes, stirring occasionally.
Taste and season with salt as needed, then serve.