Put the butter in a saucepan and, when melted, mix in the flour. Pour in the hot milk, season with salt and nutmeg and work with a wooden spoon into a smooth paste, on a slow fire. Remove from the fire and, when cool, mix in the eggs and the cheese. Divide the paste in half, and mix one half with the spinach, previously boiled, well drained and rubbed through a sieve. Drop small lumps of the alternate green and yellow paste into boiling stock through a piping funnel.