This is an obscure but very cute animated short titled The Mad Baker. I have not seen it since the mid-1970s and details are sketchy in my mind (and there is not a lot about it online) but the line about the the jelly being sucked out if the jelly donuts is there. Another bit of dialog you may remember:
“Strange little chap; he hardly seems human.”
He’s not; I baked him
The description from the link above matches what you remember:
In this parody of classic Frankenstein and Dracula films, a vampire-like "mad baker" lives in a spooky castle. His main creation is a monstrous chocolate cake which comes to life and eats its creator.
Around 20 years ago I contacted the director to see if this film was available on any media other than celluloid film. At the time, he was not willing to risk it going online. I too would love to see it again.