This is an old family recipe of mine! I haven't gotten a chance to test it myself, but I'm plenty confident in my Great-Grandma's cooking abilities. It's a great use for both sour milk and brown bananas, exactly my kind of recipe!
Mix shortening, sugar and eggs until creamy.
Mash bananas. Add bananas to egg mixture and stir.
Add milk, then rest of the ingredients. Mix well.
Bake at 350° for 1 hour.