The Truth

Feat, legendary
Prerequisite: you must perform a special ritual, the knowledge of which is granted by extraordinary means, you cannot get this feat without doing this ritual
In return for a great sacrifice, few are granted the power of The Truth

You have given up a part of yourself, or something of great value to you. (what that is is up to the DM), which cannot be restored by any means short of a wish spell.

The Truth is forbidden knowledge which grants anybody who learns this truth supreme arcane insight into the true workings of the world, allowing them to draw on the well of eldritch power that fuels magic in the world, for a price.

If you are not already a spellcaster, upon acquiring this feat, you also gain one level in sorcerer(at the DM's discretion)

The Truth allows you to restore spell slots as an action for the combined level of all spell slots restored you take 1d4(+half proficiency) necrotic damage and any damage taken in this way cannot be restored by healing magic or potions of any kind. The only thing that can restore the lost heath is (1d4) long rest, a wish spell, or greater restoration.

You can cast one spell as part of the same action, only using spell slots that you have restored, spells cast this way ignore casting time and instead can be cast as an action.

A lesser mind would crumble at what I've learned, for once in my life- I truly understand our place in the cosmos, and I can feel the arcane web binding the world.