Fry the onions in the butter, until reddish brown. Then add the flour and stir until browned, gently; do not burn. Put the boiling water in gradually stirring perfectly smooth, and adding the salt and pepper; mix well and boil one minute. Then pour it into the kettle and set back. Before serving, add the milk, warmed, and rubbed with mashed potatoes until they are smooth paste. Simmer a few moments. Have the pieces of toast ready in the tureen and pour in the hot Soup. A Puree of Onions is made by pressing the ingredients through a sieve and returning to the fire a few moments. Serve hot.