Yabia Omer: This whole thread has to do with children hiding all the matza before Motzi Matza and the subsequent question specifically asked by the OP had to do with substituting egg matza for motzi matza. So when you made your comment it was in the context as a response to what I wrote above. As stated by Rabbi Eli Gersten (OU) in his article “Who can eat Egg Matzah” “According to the Shulchan Aruch, dough made from flour mixed with fruit juices or eggs will not become chametz no matter how long it stands, provided no water is added. Despite this ruling, Ashkenazic practice mandates that egg matzot may only be used by the elderly and the infirm…………..Although the allowance to eat egg matzah over Passover applies in the above-mentioned cases, one cannot fulfill the mitzvah of eating matzah on Seder night with egg matzah. The Torah refers to matzah as “lechem oni” poor man’s bread, because it is made solely from flour and water, the simplest of ingredients. Egg matzah is called “matzah ashirah,” rich man’s bread, for it contains more complex ingredients and is unacceptable for the mitzvah of matzah. ” And yes we realize the halacha for sephardim is different.