When an artificer uses its action to create two Cannons, how can it easily expend a spell slot between the creation of the first and second cannon?

Question

While writing an answer for this question I came across a problem with how the Eldritch Cannon and the Fortified Position features interract.

Eldritch Cannon states:

Once you create a cannon, you can't do so again until you finish a long rest or until you expend a spell slot of 1st level or higher.

Fortified Position states:

You can now have two cannons at the same time. You can create two with the same action (but not the same spell slot), and you can activate both of them with the same bonus action.

I use an action to create two cannons:

• Cannon#1 is not a problem. It's either the first cannon I'm creating since I took a long rest, or I expended a 1st level spell slot some time prior to the current action.
• Cannon#2 is a problem. I have not taken a long rest, nor have I expended a 1st level spell slot since creating cannon#1.

The Eldritch Cannon feature doesn't provide me with a way to expend a spellslot, but it prevents me from creating a second cannon before I expend a spellslot.

The Artificer has no means to expend a spell slot other than to cast spells. So I need to somehow cast a spell in the middle of my action.

My understanding is that I cannot generally break up my action with a bonus action, so I cannot expend a spell slot by casting a bonus action spell between the creation of two cannons.

A reaction can interrupt an action so it could occur between the creation of two cannons, but getting the opportunity to cast a reaction spell at the right time seems excessivily unlikely and difficult.

Therefore my question is:

When an artificer uses its action to create two Cannons, how can it easily expend a spell slot between the creation of the first and second cannon?

Answer 1

Creating the second cannon costs you a spell slot

The artificer seems to be worded extremely poorly, but as it's currently written, RAW you get one cannon per long rest for free, and that summoning a new one requires you to expend a spellslot, either by casting something before you create a second cannon and expending a spell slot that way (and thus, without casting), or by sacrificing it for the cannon. (Which RAW isn't possible)

However, that is all this is, it's a poorly worded feature, which isn't what was intended.

Artillerist artificer's Eldritch Cannon feature says, "Once you create a cannon, you can’t do so again until you finish a long rest or until you expend a spell slot of 1st level or higher." In response to a question about whether spending a spell slot on anything else is sufficient to create a new cannon, Crawford replied: "Eldritch Cannon does let you spend a spell slot to create the cannon. That slot must be spent specifically on the cannon, not on something else." (From this tweet)

(See also this question)

So:

• If you've not made a cannon yet since your last long rest, it costs you 1 spellslot to summon 2 in a turn.
• If you have already made a cannon since your last long rest, it costs you 2 spellslots to summon both cannons at the same time.
• Casting a spell somewhere inbetween doesn't do anything for the cannon.

Answer 2

You expend the spell slot(s) to create both of the cannons as one Action.

According to the Eldritch Cannon class feature:

Once you create a cannon, you can't do so again until you finish a long rest or until you expend a spell slot of 1st level or higher.

That is to say, you expend a spell slot to refresh the ability to create a cannon; simply casting a spell is not sufficient for this purpose. This is similar to a Sorcerer expending a spell slot to create Sorcery Points, or a Paladin expending a spell slot to perform a Divine Smite.

The Fortified Position modifies this ability by allowing you to create two Eldritch Cannons with the same action, but not with the same spell slot. As a result, if you haven't yet created a cannon for the day, you can create two cannons for the cost of one spell slot of 1st level or higher, and if you have, you can create two cannons for the cost of two spell slots of 1st level or higher.