Why do my éclairs always collapse after baking?

Ah that's super frustrating! Usually it's a combo of problems - either your oven isn't hot enough (you really need 200°C minimum), or you're taking them out too early before they're properly dried inside. The thing that changes everything is making a small slit on the side with a sharp knife as soon as they come out of the oven to let the steam escape slowly, and then you let them cool down with the oven door slightly open! That creates a really crispy shell instead of a soft one, I swear it'll be game-changing for you.