According to St. Augustine, where did the bread come from?
From St. Augustine’s Sermon 272: (http://www.earlychurchtexts.com/public/augustine_sermon_272_eucharist.htm)
Remember: bread doesn’t come from a single grain, but from many. When you received exorcism, you were “ground.” When you were baptized, you were “leavened.” When you received the fire of the Holy Spirit, you were “baked.”
That is, we, the baptized, are baked into one big loaf of bread!