Soak cashews in boiling water for at least 1 hour. Saute onion until well browned, then add garlic and saute 2-3 minutes more. Combine drained cashews, half of the onion mixture, milk, yeast, salt and a few pieces of artichoke in a blender. Blend until smooth. Add blended mixture back into the pot with onions, artichokes and spinach. Bring to boil while stirring. Serve warm.