The Idaho potatoes are cut fresh every day, long and thin. The restaurant buys them from a distributor who ensures uniform size and quality. The vegetable oil in which they are fried is changed daily. "And we make every batch to order," says manager Patricia Ferraro. After all, the restaurant has a reputation at stake that precedes its three-year existence on South Beach. The flagship Joe Allen on Manhattan's 46th Street is 35 years old. Sister restaurants in Paris and London both boast more than twenty years. And among them all are certain simple, signature American dishes: the calf's liver, the sirloin, the hamburger, and, of course, the French fry (which, grouped as a serving, costs $3.50). Joe Allen is open from 11:30 a.m. to 11:45 p.m. daily.