Hidden inside a cute recipe book is the power to unlock recipes without the need to complete career tracks etc. It unlocks not just food recipes but also fabricator furniture recipes and spells/potions!
The cookbook itself is BGC but you can only unlock recipes for the packs you have.
Once you have unlocked recipes it cannot be undone, so make sure you really want to unlock them!
Some recipes require your sim to have a certain skill level in order to cook them – unlocking the recipes will not fulfill that requirement.
There is not a good way to display unlockables so it may appear as if nothing has happened, but I promise you it has. You can check by looking at the spell book, fridge, or fabricator.
Once you have unlocked a set of recipes, the interaction will remain available on the cookbook (for other sims to use). If I find a better way to disable it for a specific sim I will add that!