I have been thinking that the after blessing after pizza and all kinds of cake if one has eaten more that the volume of three or four eggs is birchat hamazon which is for after bread. The reason is it is either פת הבאה בכיסנין [bread that comes in pockets] or just plain bread. And even if it is  פת הבאה בכיסנין, after an amount the equals three or four eggs, it is birchat hamazon anyway. Three or four eggs volume is the amount of a full meal.--as we see in the laws of tithes where the amount of a full meal makes the obligation of taking the tithe to come into force. [If three or four eggs is an argument between Rashi and the Rambam.]]