In a large bowl, combine butter, sugar, vanilla, and eggs.
Add in 1 cup of flour, baking powder, baking soda, and salt. Mix well.
Add in last cup of flour and mix well.
Mash bananas in separate small bowl and add to mixture. Mix well.
Spray inside of crockpot with a cooking spray.
Pour mixture into bottom of crockpot and smooth out.
Place a layer of 2 paper towels across top of crockpot and place lid on top. (The paper towels will absorb a lot of the moisture from lid so it doesn't drip back into the cake.)
Cook on low for 3 1/2 - 4 hours. If batter is thin check back around 3 1/2 hours to check for doneness.
Once done, drag the side of a butter knife along edge of bread to loosen from sides.
Tip crockpot to the side and let bread fall out onto a plate.
Serve and Enjoy!