Heat a skillet over medium heat, then add the sausages to cook. Tip: Most sausages will render out some oil to help with the frying. Depending on the sausages that you select, you may need to add a small amount of oil or a shallow layer of water to stop them from sticking to the skillet.
When the sausages are almost cooked all the way through, add the sliced onions. Cook until the onions are starting to brown.Tip: Depending on the size of the sausages, skillet, and type of heat being used, it can be much easier to remove the sausages while thickening the gravy, then return just before the 5-minute simmer.
Add the diced garlic and stir until it starts to brown then add the beef stock. Let it come to a boil.
In a cup mix the water, corn starch, and gravy mix until smooth.
Slowly pour the gravy slurry into the boiling stock. Stir until thickened and again boiling. Reduce to a simmer and let gently bubble for 5 minutes.