BROWN: Heat a large cast iron skillet over medium heat. Add oil and cook sausage until browned, about 5 minutes. *If using fresh sausage (as opposed to smoked) remove sausage from the casing. Make sure to break it up into smaller pieces while cooking. Remove cooked sausage from the pot and set aside.
ROUX: Turn heat to low. Add butter to the pan to melt and whisk in flour a little at a time. Cook while stirring for about 5-10 minutes to form a medium light brown roux, scraping up any browned bits as you go.
SAUTÉ: Add sausage back to the pot with vegetables and turn heat back up to medium. Sauté vegetables for about 15 minutes until soft. Add in garlic and cook for another minute while stirring.
SIMMER: Slowly whisk in beef broth until there are no flour lumps. Simmer for about 10-15 minutes until gravy has thickened to desired consistency. Add cajun seasoning as needed. Top with fresh herbs.
Notes
Substitute andouille for pork sausage, hot sausage, Italian sausage, or chorizo. Fresh or smoked sausage works. Remove casing from fresh sausage.
Storage: Store leftover gravy in an airtight container in the refrigerator for 3-4 days.
Freeze: This gravy freezes well. Store in a freezer safe container for up to 6 months. Defrost in the refrigerator overnight or in a bowl of cold water.
Reheat: Reheat over medium heat in a skillet while stirring. Add a splash of broth to loosen the gravy up, as it will thicken as it cools.
Make ahead: Make this gravy 1-2 days in advance and store in the refrigerator until ready to use.