Prepare the Base:
In a medium saucepan, melt the butter over medium heat.
Add the finely chopped onion and cook until it becomes translucent, about 5 minutes.
Add the minced garlic and cook for another 1-2 minutes until fragrant.
Incorporate the Liquids:
Stir in the red wine (if using) and cook for 2-3 minutes, letting it reduce slightly.
Add the beef broth or stock, Worcestershire sauce, soy sauce, bay leaf, dried thyme, and dried rosemary. Stir to combine.
Simmer:
Bring the mixture to a boil, then reduce the heat and let it simmer for about 20-30 minutes, allowing the flavors to meld together. Stir occasionally.
Thicken:
If you wish to thicken the au jus a bit, you can mix 1 tbsp. of flour with 1 tbsp. of water and then add it to the au jus. Alternatively I like to mix 2 tsp. of Trio Gravy Mix with 2 tsp. water and then add that to the au jus. It thickens just a bit and adds a more depth of flavour.