1. Place a heavy bottom skillet (such as cast iron) over medium heat. Place a large skillet with 2 tablespoons butter over medium heat. 

2. Place the bacon in the warming heavy bottom skillet and cook, turning frequently, until it reaches desired crispness, between 7 and 10 minutes. 

3. Once the butter in the large skillet has melted, add the sliced onion and sauté, stirring regularly, for about 15 minutes. 

4. While the bacon and onions cook, slice the mushrooms. Then combine the ground beef, parsley, onion, garlic, salt, and pepper in a mixing bowl. Form into four equal patties. 

5. Once the bacon is done, transfer to a plate and drain all but about 2 tablespoons of bacon fat from the skillet. Add the burger patties to the skillet, reducing heat if the bacon fat starts to smoke. Cook patties for about 4 minutes per side, or until desired level of doneness. After the onions have cooked for about 15 minutes, add the sliced mushrooms and continue to sauté until ready to serve.

6. After the onions have cooked for about 15 minutes, add the sliced mushrooms and continue to sauté until ready to serve.

7. Toast the burger buns, spread each side with mayo, and top each burger with one quarter of the sautéed onions and mushrooms, and one slice of bacon. Serve immediately. 

Want to Make it Vegetarian?

For the burger use 2 packages of Beyond Meat Burgers!