To make cashew sour cream, blend together 1 cup of soaked raw cashews (in warm water at least 30 mins, drained), 1 T. lemon juice, a pinch of salt, and about ⅓ cup of water. Add more water if too thick. Use to spoon on top of the casserole, or put it in a sandwich bag, cut off a small corner, and drizzle on each serving.
This casserole freezes well, so try making two at once so you have one for later!