Once per battle, when you cast a spell that targets Physical Defense, before rolling for the number of targets or making the spell's attack roll, you can expend your quick action to evoke the spell. Hit or miss, you'll max out the spell's damage dice (except on a natural one, which deals no damage to the target and likely damages the caster in some manner).

Champion Feat: 

Whenever you evoke a spell, you can reroll one of the attack rolls if that natural roll was less than or equal to the escalation die. You must take the new result.