At 11th level, you discover a magical secret called a Greater Formula. Choose one 6th-level spell from the apothecary spell list as this formula.
You can cast your Greater Formula once without expending a spell slot. You must finish a long rest before you can do so again.
At higher levels, you gain more apothecary spells of your choice that can be cast in this way: one 7th-level spell at 13th level, one 8th-level spell at 15th level, and one 9th-level spell at 17th level. You learn an additional 6th-level spell at 19th level, and an additional 7th-level spell at 20th level.
You regain all uses when you finish a long rest.
Master Reformulation. Whenever you finish a long rest and consult your formula book, you can replace one spell you gained from this feature with another spell of the same level from the apothecary spell list.