I think your friend may be referring to Mostarda di Frutta which is an Italian fruit preserve spiced with mustard essential oil. The mostarda generally has a mix of whole or chopped candied fruits such as cherries, figs, plums, pears, peaches and tangerines which are added to the mustardy, sweet syrup.
I've generally seen it at fancier Italian food stores around Christmas time.
Jyoti
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Ruhlman