Score each row of kernels with a sharp knife, and scrape them and the milk from the cobs. Cook the onion in the butter until soft but not brown. Add the flour and the corn, and stir until the mixture starts to thicken. Transfer the mixture to a double boiler and gradually add the milk stirring until cooked – then season to taste with salt and pepper. Serve hot, garnished with lots of finely chopped parsley and a small additional pat of butter.