In a medium heavy-bottomed saucepan, heat the oil over medium. Stir in the onion and sauté over medium heat until the onion softens, about 4 to 5 minutes. Add the garlic and wine and cook for another minute or so.

In a medium bowl, whisk together the broth, mushroom powder and rice flour until blended. Pour into the pan and stir in the tamari, nutritional yeast, and pepper. Bring the mixture to a simmer over medium heat, whisking frequently, until the gravy starts to thicken. Reduce heat to low and cook for a couple minutes.

Once the gravy has thickened, remove it from the heat. Pour the gravy into a blender. With the lid ajar (so steam can escape), blend on low to medium speed until the gravy is smooth.

Transfer the gravy back into the pot and keep warm for serving. Like most sauces, the gravy thickens a bit as it cools. Store cooled leftover gravy in an air-tight container in the fridge for up to a week.