At least 2nd level, probably much much higher
For a baseline, compare the Pearl of Power. This uncommon magic item, requiring attunement, can restore one spell slot, of low level, for one character. It is clearly much less powerful than the spell you describe.
The DMG (p.128) suggests that a magic item can only be created by a spellcaster who can cast any spells the item produces, and further gives guidance that 3rd level is a reasonable point at which a character could create an uncommon magic item. From this we can gather that the effect of a Pearl of Power, much weaker than Brew, should be about a 2nd level spell (available to a 3rd level caster.)
But you are creating something much more powerful. It restores all spell slots, including the one used to cast it, and does so for an entire party, as well as all class features (not to mention the HP restored.)
There's not much guidance for what level this spell should be, since for the most part, 5th edition does not allow this type of repeatable resource renewal. I'd suggest that if you allow this spell, it must have a material cost, otherwise it will essentially always be used. There is precious little reason not to do so. Further, I'd suggest that the brew created must expire at some point. Otherwise, it might as well not cost any resources at all, since it can simply be created and saved during downtime.
Based on very little precedent, I'd also recommend this being a level 9 spell. At any other spell level, there is too little cost to simply saving a spell slot for Brew. At least at 9th level, it is guaranteed that the caster will given something up in a prior encounter to be able to use it (though even then, they still have a 9th level slot after they use this spell.)
But I'd recommend not doing this
This spell causes all sorts of problems. Mage Armor (and other 8 hour duration spells) can now be used without taking a spell slot, just drink the brew after using them. Warlocks, monks, and other classes balanced around short rests are drastically weakened, whereas wizards can now pull out all the stops twice per day. Wizards can now switch their prepared spells during short rests, making them much more versatile. Only once before taking a "real" long rest, yes, but even two long rests per day is more than the game is balanced around.
In short, this spell will have extreme consequences for game balance, even at 9th level. I'm not sure it's worth doing just for the joke. I'd recommend drastically reducing its scope before trying to give it a level.
Unless the intent is for this spell to replace a long rest
If the intent is for this spell to replace your "real" long rest, then you most likely want to reword it. As written, the spell does not make your short rest become a long rest, and you are able to benefit from more than one long rest per day. If you instead clarify that this is a long rest for the purposes of the rule dictating one long rest per 24 hours, then this solves many of the problems of the spell.
 Obviously the exact effect of the Pearl of Power would be problematic on its own as a second level spell; this is just to give an example of how the proposed spell is wildly more powerful than a cantrip.