recurrence is one of the 117 mis-spellings listed as 'Common difficulties' in the section on 'Spelling' within 'Writing' in UEfAP.
As the stress in the verb 'to recur' falls on the final syllable, it follows the third of Hart's Rules on Consonant doubling: the final consonant ('-r-') is doubled before '-ing'. '-ed', and '-ence'. Hence the correct spellings are
recurred recurring recurrence - all with double '-r-'
- See also occur.