Add the butter to a medium pot and bring the heat to medium.
Add the garlic and sauté for 1 minute.
Add 2 cups water, bouillon cube, soy sauce, nutritional yeast, onion granules, dried mustard, and poultry seasoning. Stir for 3 minutes or until the bouillon cube has dissolved.
Combine 1 cup of room temperature water with the potato starch. Stir with a whisk to combine.
Pour the starch slurry into the pot and reduce the heat to low.
Cook for 15 minutes stirring frequently or until the gravy has thickened.