<noun> British slang
Male ejaculate, semen, penile ejecta, a bomb-load of jizz.
Seeing as sperm is the cause of 99.9% of pregnancies - resulting in babies - it was only a matter of time before someone made the connection between sperm and babies and formed the phrase Baby batter as a metaphor for come/cum.
See also Baby Gravy
"Jasper fired his 6oz load of baby batter into Margaret's face, and she supped it up like a glass of warm, creamy milk."