Final answer:
The common method is to cook bacon first and then cook mushrooms and onions in the bacon fat for added flavor, but this can vary based on personal preference or dietary needs.
Step-by-step explanation:
When preparing a dish that includes mushrooms, onions, and bacon, the order in which you cook these ingredients can vary based on the recipe or personal preference. However, a common method is to cook the bacon first. This approach allows the mushrooms and onions to be sautéed in the bacon fat, which adds flavor to the vegetables. If you prefer not to use the bacon fat, you can cook the mushrooms and onions separately in another type of oil, and then combine them with the bacon later. In summary, either ingredient can be cooked before or after the bacon, depending on the desired outcome and dietary considerations.