Slice or chop mushrooms and dice onions.Make vegetable broth - I make 3 cups incase I need extra for thinning especially for reheating. Add the dairy-free butter and olive oil to a medium skillet over medium-high heat until melted. Saute the onions for 5-7 minutes until turning golden and caramelizing.
Add the garlic and mushrooms to the onions. Cook for another 5-7 minutes while the mushrooms release their water and start to turn golden.
Stir in the sherry and cook for another minute or two while it reduces.
Add 3 tablespoons of butter and stir to incorporate while it melts.
Add all the flour* stirring to incorporate for 2 or 3 minutes while a paste forms (roux) and sticks to the mushrooms.
Add 1 cup veggie broth, mushroom powder, and sage and onion seasoning - whisking to incorporate. Add the remaining 1 cup broth and whisk until smooth and lump free. Once the gravy starts to thicken, reduce the heat to simmer (low) and stir as needed.
Taste and adjust seasoning (salt, pepper and fresh thyme). This is when you would add the soy sauce only if needed for flavor.