Chop up the celery and onion, and finely mince the garlic.Heat the olive oil in a large pot over medium-high heat. Add the celery, onion, and garlic and sauté for about 5 to 10 minutes until the celery and onion begin to soften and look translucent.Add in the vegetable broth, water, then slowly pour in the flour as you whisk the soup to avoid any lumps. Add in the bay leaf, thyme, and raw cashews. Bring to a simmer and cook for about 15 minutes until the cashews are very soft.Remove the bay leaf, then blend in small batches, being careful not to fill your blender too high so it doesn't erupt. If you don't have a high powered blender such as a Blendtec, make sure to blend very well so that the cashews are completely blended.Return to the pot to heat or serve directly from the blender. Season with salt and pepper if desired and garnish with some celery leaves.