Heat the olive oil in a large, deep, heavy-based frying pan over medium heat. Add the sausages and cook, turning frequently, for 6–8 minutes or until browned on all sides and cooked through. Remove the sausages from the pan and set aside.
Spoon out any excess oil from the pan, leaving at least 1 tablespoon. Add the onion and cook for 3–4 minutes, stirring occasionally, until softened.
Stir through the minced garlic for 30 seconds, then add the butter.
Once the butter has melted, add the flour and stir to combine to create a paste. Cook for 1 minute.
Add half of the beef stock. Use a whisk to stir continuously to avoid lumps. Add the remaining beef stock, continuing to whisk, and bring the mixture to a simmer.
Add the thyme leaves (if using), Worcestershire sauce, black pepper and salt to taste. Simmer for 2–3 minutes to thicken (if your gravy is too thick or too thin, see note 4).
Return the sausages to the gravy and serve immediately with mashed potatoes and steamed greens.
