The Long John is a bar-shaped, yeast risen pastry like a doughnut either coated entirely with glaze or top-coated with cake icing.They may be filled with custard or creme.The term Long John is used in the Midwestern U.S. and Canada, and has been used in Texas.. In other parts of the United States, such as the Mid-Atlantic, Long Johns are sometimes marketed as “éclairs”; the two pastries look …