John Lightfoot on Matthew 15:36

[He gave thanks and brake.] See here the tract Beracoth, where it is discoursed of the manner of giving thanks when many ate together: Three who eat together ought to give thanks together: that is, one gave thanks for the rest (as the Gloss writes) "in the plural number, saying, Let us give thanks." So when there were ten, or a hundred, or a thousand or more, one gave thanks for all, and they answered after him Amen, or some words which he had recited.