The punchline is close to the literal meaning of the phrase "You can't have your cake and eat it too."
Sousai Shoujo Teien Activity DiaryWow...could these be cookies from Emma!?They both enjoyed them afterwardsAnd handmade!?We couldn't bring ourselves to eat them because it would seem like such a waste to eat (what you created)!
The phrase doesn't seem to translate smoothly into English, so I tried to convey the intent.No way...
I'm going to cry...Inedible CookiesEhehe...Eat them!That night, by messageHow did you like them?You two...
Here...If they were plastic, we would keep them forever!!Eh!? What!?
Presents!?You mean PVC was the solution!?