Cut the bread into thin slices and put them into a saucepan, adding water and some salt. Put the saucepan over heat, and when it boils add the egg white. Cover it and shut off the heat, leaving it to rest on the hot surface but not to boil.Separately, beat the egg yolk with a little salt and some drops of lemon juice. Little by little add oil to make mayonnaise. Once made, add water from the soup to temper it and so that it doesn't curdle when you add the rest.Gazpachuelo can be eaten hot or cold, according to taste.