Place the cashews in a small bowl and add boiling water to cover. Soak for 1 hour, then drain. (Alternatively, soak the cashews in room-temperature water to cover for at least 6 hours or overnight, then drain.)
Preheat the oven to 350°F (180°C).
Chop 3 cloves of the garlic and add to a high-speed blender along with the cashews, water, tapioca powder, tahini, nutritional yeast, apple cider vinegar, salt, and miso. Blend on medium-high speed until smooth, about 1 minute.
Pour the cheese mixture into a 7½ x 2-inch round brie baking dish. Thinly slice the remaining 3 garlic cloves and arrange them on top of the cheese. Sprinkle with the thyme. Bake, uncovered, until the cheese has formed a skin on the top and is lightly brown around the edges, 25 minutes.