In a large measuring cup or a small bowl, combine 2 cups hot water with the dried mushrooms, then allow to sit for at least 10 minutes.In a medium-size pot, warm the olive oil over medium heat. Add the onion, fresh mushrooms, garlic, thyme, salt & pepper. Pour tamari over top, stir to combine and cook for 10 minutes, until the mushrooms are tender.Next, separate the dried mushrooms from the liquid (reserving the liquid for later), chop them into small pieces, and then add them to the pot with the cooked fresh mushrooms. If you like a chunkier gravy with mushroom pieces, separate some (1/4-1/2 cup) of the fresh mushrooms out of the pot at this point.Add the arrowroot powder to the cup with reserved mushroom liquid and whisk until smooth. To the pot, pour the reserved mushroom liquid and vegetable broth. Bring to a low boil then lower heat and allow to simmer for 5 minutes, until slightly thickened, while stirring intermittently. It is very important that you don’t cook it at too high of heat or for too long otherwise it will break down the thickening properties of the arrowroot. Remove from heat and set aside to cool.Once cool, add the contents of the pot to a blender and blend until smooth. Stir in fresh mushrooms that you set aside then transfer to a bowl for serving.