After coming home from Dairy Queen, your friend, relative, or significant other puts their DQ Blizzard in the freezer for later. You pull a fast one and ejaculate into their Blizzard mix it around and put it back.
Jillian: Charlie, I'll be right back, I have to pick up my mother at the airport. Can you take care of the dogs and please don't eat my Dairy Queen!
Charlie: Yeah no problem.(Takes out phone to call Frank)
<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."