Heat butter over medium heat until melted
Add onion and sautee until softened
Add garlic and sautee onions and garlic until onions are translucent and start to brown a little
Whisk together tomatoes, vinegar, mustard, honey, and spices
Add tomato mixture to onions and garlic
Simmer mixture for 10 minutes
While sauce is simmering, form burgers into patties
Salt & Pepper both sides of the patties
Add burgers to sauce
Turn heat to medium-low
Cover pan and simmer for at least 30 minutes - flipping halfway through cooking. You can simmer these for up to 90 minutes for maximum flavor (be sure to keep an eye on the heat, you may need to turn it down lower for a longer cooking time)
Top with cheese, if using, about 10 minutes before serving