Secret Recipe
Strategy
The Secret Recipe is secret.
Reset all your attributes and do NOT spend any points (if you really want to, max Wisdom and Empathy, but spell charge time is not an issue even without).
Pick spellhound as a pet.
Do NOT buy ANY upgrade beside the spell slots. They are useless for the purpose, and harmful if you by chance buy summoning efficiency ones.
Every time you cast a spell you either hear a sound, which means you found the right "next ingredient" or you hear nothing, in which case you are restarting the whole process and need to repeat the sequence of correct ingredients up to the point you failed.
Use the spells with the shortest duration for each category. You are simply trying to find a hidden sequence of spell types (colors), and what matters is the cast, so a long duration is just a waste of time.
It's the easiest challenge there is.
Note: If you restart the challenge the recipe stays the same, even if you win. In my case it was 4 incantation followed by 1 summon.