Can a sorcerer use the Quickened Spell metamagic option to cast cantrips?

Question

Considering that in higher levels, cantrips deal more damage than L2 spells (especially if you dip 2 levels of Warlock, with EB + Hex + Agonizing Blast), I'm wondering whether it's more efficient for an (MC) Sorcerer to use L2 Slots to power Quickened (EB) cantrips.

The Quickened Spell metamagic option says:

When you cast a spell that has a casting time of 1 action, you can spend 2 sorcery points to change the casting time to 1 bonus action for this casting.

The idea would be to Quicken EB a few times (or in a big fight, until you run out of SP), and at the end of the fight (or during, if needed), convert L2 slots to more SP. Since you keep these until a long rest, you can basically stock up in SP in between fights.

Can a sorcerer use the Quickened Spell metamagic option to cast cantrips?

Answer 1

Yes, as long as the cantrip has a casting time of 1 Action

Most cantrips require an action to cast. As such, you can certainly quicken them. So any 1 Action casting time cantrip will be usable, such as Eldritch Blast in this question.

However, PHB p. 202 states:

A spell cast with a bonus action is especially swift. You must use a bonus action on your turn to cast the spell, provided that you haven't already taken a bonus action this turn. You can't cast another spell during the same turn, except for a cantrip with a casting time of 1 action.

Thankfully, if you are planning on casting two cantrips per turn, you are more than able to do this effectively, as they are not restricted by the same restriction as regular spells.

Answer 2

Yes, you can use Quicken Spell to cast cantrips. As you've noted, Quicken Spell requires a spell with a casting time of one action. Cantrips are defined as:

A cantrip is a spell that can be cast at will, without using a spell slot and without being prepared in advance. Repeated practice has fixed the spell in the caster’s mind and infused the caster with the magic needed to produce the effect over and over. A cantrip’s spell level is 0.

There is nothing here that would prevent cantrips from being usable with Quicken Spell, so as long as the cantrip in question has a casting time of one action (which Eldritch Blast does), you can use Quicken Spell to cast it as a bonus action.

You've probably noticed, but I'll point out for readers, that this means you can cast two Eldritch Blasts in a single turn, since the restriction on bonus action spells is:

You can’t cast another spell during the same turn, except for a cantrip with a casting time of 1 action.