Primordial Caster A5E

Upon gaining this feat, choose one of the following damage types: acid, cold, fire, lightning, or thunder.

When you cast a spell that deals damage, your spell’s damage ignores damage resistance to the chosen type.
When you cast a spell that deals damage of the chosen type, you deal 1 additional damage for every damage die with a result of 1.
This feat can be selected multiple times, choosing a different damage type each time.

Source: Adventurer's Guide (EN Publishing) · License: Creative Commons Attribution 4.0 / OPEN GAME LICENSE Version 1.0a details