What was the miracle of Blessed Luigi and Maria Beltrame Quattrocch? Luigi and Maria Beltrame Quattrocch were beatified by Pope John Paul II.  They were the first married couple to be beatified.  They lived exemplary lives in Fascist Italy during WWII; but I can't find any information regarding a miracle being attributed to them.  For canonization, there must be demonstration of two miracles, one of which must be posthumous.  I thought demonstration of one miracle was required for beatification.  However, I may be mistaken about that detail.
That took some digging, but I found it (at the National Catholic Reporter no less)


  A miracle — the prerequisite to any beatification — is attributed to the couple. It involves the cure of a young man suffering from a severe circulatory disorder. He is now a 35-year-old neurosurgeon in Milan.


http://natcath.org/NCR_Online/archives2/2001d/122801/122801a.htm

A miracle is not necessary for beatification if they're martyred, but the couple wasn't Martyred. 

There is another couple who has recently been beatified, St. Therese of Lisieux's parents 
Bl. Louis Martin and Bl. Marie-Azélie Guérin.  Apparently in cases of Married Blesseds, which there have not been many, the faithful can pray for their intercession for a join miracle, that's pretty neat.