Mother made a batch of bean soup, and then baked some, but not boston style. She mashed them and then baked?!
She probably has a family recipe or one she's honed on her own.
I don't know about the mashing part but I make one similar to this.
You wouldn't have to use all the different types of beans in this recipe and use just one kind.
Southern Bean Soup
A great soup to make when you find yourself with leftover baked beans.
It is better to drink bean juice.
if you could ask Mom
or a relative might know her secret