Turn the heat to medium and place a small pan on the stove.
Add the butter and some drippings to the pan.
When the butter and fat are heated, add the chopped onions and sauté for 3 minutes until the onions are translucent.
Now add the mushrooms and let them cook for another 2 minutes.
Add the flour. Cook constantly, stirring, until fragrant and light brown. About 2 minutes.
Add the beef broth, continually stirring a little at a time, so no lumps form.
Add the rest of the drippings. Let the gravy cook and thicken. Approximately 7 minutes.
Pour into a gravy boat to serve with your favorite roast.