Don't buy the wallpaper/tile to active the side goal right away. You can cook the recipes before you even start side goal. Because once you've completed side goal they'll go away from basic oven to their original appliance.
It's 82 servings to mastery, and @AnniraSweets is awesome at posting all the steps ahead of time, so it's easy enough to add up total amount of servings from each recipe required in side goal. If it's less than 82 then cook whatever the difference is before you activate goal. I did this for Moon Pie only, since I don't have the Nursery Rhyme Oven it's originally from. Note this only if you want to earn gems for mastery.
Hope this helps 🙂
Edit----This only applies to next future side goals, sorry about this completed one 😕