“You can’t have your cake and eat it, too.”
Don’t be silly. Of course you can.
If you eat it, you still have it; it just changes form and location. You still possess it.
“How to put this delicately? This time tomorrow, you probably won’t still have it.”
You didn’t say anything about having it forever. Point is, you can indeed eat it and still have it. For a little while. Besides, all the ingredients will break down and nourish various parts of you. All those little milk molecules and egg atoms will be with you for quite some time.
Anyway, doesn’t having it mean eating it?
“I’m not following.”
If Aunt Bessie says, “Here, have a piece of cake,” is she expecting you to just sit there and stare at it, or does she intend for you to eat it? Be kind of rude not to. You cannot “have a piece of cake” without eating it.
“Just never mind, okay?”