This year, Stutz will box up more than 5,000 pounds of its Irish potatoes. Outside Pennsylvania, though, the candy is either hard to come by (all 1,000 pounds of Irish potatoes made by Chicago's Fannie May Candies, for example, are shipped east) or unrecognizable (See's Candies of San Francisco dusts its with lots of cocoa and puts walnut-filled divinity inside). To avoid such ''impostors'', many addicted Philadelphia transplants (and Philadelphians) either mail-order from a reputable local producer or make their own. Family recipes have been handed down for generations, and variations are staggering. Most experts agree that coconut is essential for the classic version, but the center can be made with real mashed potatoes, or with that other familiar Philly favorite, cream cheese.