The phrase "bottom of the mixing bowl" means a person or thing that is the lowest or least important in a particular group or situation. Full definition
I always seem to have a bunch of cream cheese at the very bottom of my mixer bowl that doesn't like to mix in, so I have to make sure it is all incorporated. (tasteandtellblog.com)
(You can speed this up by pressing bags of frozen fruits / veggies against the sides and bottom of the mixing bowl. (iwasborntocook.com)
It let it hang like that for three to four hours and drain the liquid that has collected at the bottom of the mixing bowl. (seitanismymotor.com)