I've heard that there are those who hold that saying a bracha rishona (ie the bracha usually said before eating) after you have eaten a food is effectual. Where might I find a source that says that?
(For example, you ate an apple and as just as you swallowed the last bite you remembered that you did not say borei pri ha-etz before you started eating. You then say borei pri ha-etz, even though you are done eating.)