Place cubed challah on a lined baking sheet and bake on 350 degrees Fahrenheit for 20 minutes until crispy.
Heat oil in pan, then cook onions, celery, and sausage until browned. Add broth and bring to a simmer.
Pour broth mixture over challah croutons. Combine well.
Add eggs and parsley and stir together gently so as not to break challah.
Place in muffin cups and bake on 350 degrees Fahrenheit for 20 to 25 minutes until the muffins are set and the tops are slightly crispy. Serve with mushroom gravy.
Melt margarine in pot, then add mushrooms. Cook until tender, then add flour. Combine well.
Add broth and stir over medium heat until thickens.
Serve over challah sausage muffins.