Mix together the sugar, cornstarch and salt in a small saucepan.
Mix together the eggs and milk, and stir this into the sugar mixture, whisking
to dissolve the sugar and eliminate lumps. Heat over moderate heat, stirring almost
constantly, until the mixture has thickened, about 10 minutes.
Stir in the butter and vanilla extract. Pour the mixture into a bowl or 4 to
6 small individual bowls.
Place plastic wrap directly on the surface of the pudding
to prevent the formation of a "skin" and refrigerate until thoroughly
chilled, at least 2 hours.