masturbate while breaking fast

On one occassion I remembered that I masterbated because I had too much desire and then I ate a date thinking that my fast was broken anyway. My memory from Maktab was that as my intention to masterbate was not to eat but was because of desire so therefore only 1 Kaza is necessary and not 60 cosequtive roza. Is one necessary or is 60 consequtive necessary.
Alhamdullilah I made Toba for this eavil actions and no longer masterbate.