Put ¼ cup of the raw cashews in a small bowl and cover with boiling water. Let soak for 15 minutes, then drain and discard the water.
Cut the leaves and core off of the kohlrabi. Then cut each one in half and peel the tough skin using a potato peeler and a paring knife for the very tough areas. Slice into thin half circles.
Slice the onion and mince the garlic.
Add 1 tablespoon of butter to a large, oven-proof skillet over medium-high. Once hot, add a layer of the sliced kohlrabi and sear each side for 2 minutes. You will have to work in batches, adding another tablespoon of butter as needed. Remove each batch when it is done, put into a large bowl, and set aside.
Put the soaked cashews into a blender with 1 cup of filtered water. Blend until smooth.
Put the remaining butter into the same frying pan and heat to medium-high. Add the onions and garlic and cook for 3-5 minutes or until soft. Then add these to the bowl with the kohlrabi.
Pour the cashew milk into the hot pan. Add the nutritional yeast, salt, and pepper. Cook on medium heat for about 3 minutes as it thickens up. Add the spinach to the pan and when it is wilted, add in the kohlrabi, onions, and garlic.
Chop the remaining cashews and place on top of the mixture. Then put the skillet into the oven for 10-15 minutes.