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.
<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.