system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do brownies get that lighter brown flake layer on top after you bake them?
gpt
Good question! What you're actually seeing on top of the brownie is a thin layer of meringue. Meringue is made by whipping up egg with sugar, but that flaky crust isn't quite the fluff you expect from a meringue. What's happening in the brownie is that some sugar is rising to the top and melting - forming a shiny surface - and the egg white is binding it all together into thin sheets.