Wondrous Item, common
Stitching together strands of shadow, you conjure forth a book in your hand at the end of a Short or Long Rest. This Book of Shadows (you determine its appearance) contains eldritch magic that only you can access, granting you the benefits below. The book disappears if you conjure another book with this feature or if you die.
On your adventures, you can add other ritual spells to your Book of Shadows. When you find such a spell, you can add it to the book if the spell’s level is equal to or less than half your warlock level (rounded up) and if you can spare the time to transcribe the spell. For each level of the spell, the transcription process takes 2 hours and costs 50 gp for the rare inks needed to inscribe it.