- Preheat oven to 350 degrees. Grease a round cake pan and set aside. 
- In a food processor, blend avocado, bananas, egg, vanilla, and milk. If you don't have a food processor, mash the banana and avocado well. Then, whisk all the ingredients together until smooth. 
- Place mixture into a medium bowl. Add flour, sugar, cocoa powder, and baking soda. Fold just until combined. 
- Spread cake batter into greased cake pan. Batter will be thick. Spread until the batter is even and to the edges of the pan. 
- Bake for approximately 24 minutes, or until the center is firm and/or a toothpick inserted into the middle comes out clean. 
- Allow to cool slightly. Then, flip cake onto a cooling rack so that the top of the cake is against the rack.