Knuckle butty - Tradução em português

Hi, friends!

I´ve tried to find the meaning of "knuckle butty" but I have found nothing specifically about.

This is the sentence I read from a brit girl with these two words:

" My boy is so cute.. He knows I'm scared shitless of bee's & 1 flys past! He turns round n says... "It's ok Mummy, if it comes again I'll give it a knuckle butty".

I presume it´s something regarding a punch or hit.

Could you please, friends, help me to get exactly the translation to these words together?

Ps.: I do love this website !

Take care,

Maria Salvador