Hello there!
So the effect of Fingers of Frost, for those who dont know;
Gives your Chill effects a chance to grant you the Fingers of Frost effect, which treats your next spells cast as if the target were Frozen. Lasts 15 sec.
As it states on the spell, it only got 2 charges. But now here is the exploit.
First you cast a normal frostbolt or whatever, then you are left with 1 charge.
On this charge you use a rapid shatter combo (Frostbolt + Ice Lance), and both will count in it.
I hope this isnt a repost, atleast I didnt find anything searching for Fingers of Frost.
I hope this helped, a little something something for the mages!