You may prepare your spells in such a way to cast multiple spells at once.

Prerequisite(s): Arcane Duality or Arcane Discipline, Caster level 9th or higher

Benefit: You may prepare two spells of the same level in a single spell slot 4 levels higher, allowing you to cast both spells at once. Casting the spells from the affected spell slot requires a full-round action. For example, you may prepare two magic missile spells in a single 5th-level spell slot, allowing you to cast both magic missiles with a single full-round action. You may not choose to cast only one of the spells from the affected slot; you must cast them both if you cast either of them.

You make all necessary decisions (such as target) separately for each spell, exactly as if you had cast them using two separate actions. Each spell must penetrate spell resistance individually, even if you cast them at the same target, and if a saving throw is required, all targets receive a separate saving throw against each spell.

If someone attempts to counterspell you when you are casting the dual spells, the counterspell attempt follows the normal rules, but only one of the two spells may be countered.