For certain types of bread-like foods, one only washes and makes HaMotzi when eating a sufficiently fixed quantity. Suppose you make a Mezonos a small amount of cake, and after finishing it you realize that you are still hungry and want to eat a lot more.
Do you eat it under the coverage of your first Mezonos? Do you say an Al HaMichya or Birkat HaMazon?
How do you say an Al HaMichya on what you would consider a full meal? How do you bench on something you made a Mezonos on?