Add the cashews to a medium bowl with enough vegetable broth to cover. Soak for at least 2 hours, or overnight. Drain and rinse.
Preheat the oven to 400˚F (200˚C).
Using a mandolin or a sharp knife, thinly slice the sweet potatoes into rounds.
Add the sweet potatoes to a large bowl and toss with the olive oil, garlic, thyme leaves, pepper, and salt.
Add the drained cashews to a blender or food processor, along with the garlic, coconut milk, nutritional yeast, lemon juice, vegetable broth, nutmeg, cayenne, and salt. Blend until smooth and creamy.
Grease a large cast-iron skillet or other ovenproof dish with oil.
Pour ⅓ of the cashew sauce into the skillet and tilt to evenly coat the bottom. Layer half of the sweet potato rounds over the sauce, overlapping slightly to completely cover the bottom of the pan. Repeat with another ⅓ of the sauce, the rest of the potatoes, and the rest of the sauce.
Bake for 1 hour, or until golden brown on top and the sweet potatoes are tender.
Let cool for 15 minutes before slicing and serving.