Does one eating a piece of cake during Sukot have to eat it in the Suka and also recite a blessing? How big should that piece be?

Mishna Berura (639: 15 – 16) mentions that for the Mezonos (cakes) eaten at the Kiddush on the mornings of Yom Tov after davening, one can recite Leishev Basuka, since that particular piece of cake is considered as a meal for the purpose of Kiddush. He adds that the common minhag is to do the same during other small meals, as long as the cake has an egg volume and one stays in the Suka some time.