In a cast iron pan over medium heat, add diced bacon and cook down. Leave grease in pan.
Add sliced onions with butter and seasonings into the pan. Once butter melts stir so onions are coated.
Every few minutes stir them so they cook down, soften, and absorb the bacon grease and butter flavors. Once they're a nice golden rich color use a slotted spoon to remove and serve immediately for best results.
Timing may vary depending on how soft and brown you want them: from 25 min to 60