Well out of the book simply eating a rare ingredient raw gives a certain effect.
Treat the class like any of the mage options with the 3 starter spells but not let them cast the spell like a mage would if they dont want to be magic. Those are the potions they can make using the rare ingredients AND they can also just consume the rare ingredients for their natural effects.
For a custom starter loot give them #30 on the magic loot table the Potioner’s Kit.
also the alchemy system from Zelda Breath of the Wild is pretty simple to adopt. Monster part + Bug.
Monster parts are kinda like POWER in spells multiplying the effect
Bugs decide the buff/debuff
Or could do it like Rare ingredient + Monster part = potion related to the monster harvested from.
Kinda like Blue mages from Final fantasy. Get a temp buff for 1d4 ROUNDS or maybe even a monster ability for the duration.
A Poisonous monster part lets you inflict poison for 1d4 Rounds or maybe be immune to poison for 1d4 Rounds or maybe straight up heal a poison condition from someone