Spelldrain Talisman

Wondrous item, Rare, Requires attunement
You gain a +1 bonus to spell attack rolls and the saving throw DCs of your spells when you use this necklace as the focus for those spells.
When you run out of spells, your next attack is empowered. After you expend your last spell slot, the next attack you make within 1 minute gains a bonus to its attack and damage equal to the level of your highest level spell slot. (This does not trigger on expenditure of non-slot spells such as magic item use, and does trigger on non-spell features that cost a spell slot.)