Preheat the oven to 400 degrees.
Boil the raw cashews for 10 minutes (or you can soak them in cool water for 2-3 hours). Then drain the water and discard it. While the cashews are boiling, prep the veggies. Mince the garlic cloves, peel the potatoes and onion, use a mandolin to slice the potatoes and onion into slices that are about ⅛ inch thick, and roughly chop the fresh spinach.
Add the softened cashews, unsweetened almond milk, low-sodium vegetable broth, garlic powder, onion powder, lemon juice, nutritional yeast, salt, and black pepper to a high-powered blender. Blend the cashew sauce on high until it’s smooth and creamy.
In a large, 9×13-inch deep casserole dish, pour a little bit of the cashew sauce into the bottom of the casserole dish and evenly spread it around. Adding a layer of cashew sauce will stop the potatos from sticking and you won’t have to grease the bottom of the pan.
Then add a layer of thinly sliced potatoes, red onions, spinach, garlic, and more cashew sauce. Repeat these layers until you run out of ingredients.
Reserve 1 cup of the cashew sauce to pour over the top of the potato casserole. I also like to save a little bit of spinach to sprinkle on top to show that it’s florentine-style.
Cover the potato casserole with parchment paper and bake it for one hour. After 40 minutes, carefully remove the parchment paper and let the casserole bake uncovered for 20 more minutes or until the top layer is golden brown.
Carefully remove the vegan scalloped potatoes from the oven and let it sit for 10 minutes to set up and cool down a little bit. Garnish with chopped chives or green onions and enjoy!