
Loreguard |

So each lesson has a Key spell which the witch learns along with the lesson. (in addition to the Hex)
Wouldn't it make it thematically more interesting if you could spontaneously cast your lesson spells? So you would prepare your spell slots with other prepared spells, but could replace any slot with a lesson spell, spontaneously.
Lesson spells could then never be lost because of a familiar died, because they aren't prepared spells, and would be available the first day after a replacement familiar is summoned.
Or, if you feel that is too 'significant' an advantage, limit it to only if that lesson spell has been memorized in one slot. (or one slot at that level) That would mean if you memorize one use of the lesson spell, you could spontaneously cast it additional times using up other slots that you had other spells memorized in.