I’ve been staring at a can of that in my pantry ... what’s a clabber?
Clabber was the word used for soured milk. Not rotten gone bad off the shelf milk but fresh from the cow milk that had been allowed to sour. It was called for in a great many recipes in my grandmother’s day. You can substitute buttermilk or a mix of yogurt and milk.
“Clabber Girl” is a baking powder. I don’t use that brand because it has aluminum.