Three years ago, I published a series of articles about how to create a framework on top of the Symfony components on this blog.
Along the years, its contents have been updated to match the changes in Symfony itself but also in the PHP ecosystem (like the introduction of Composer). But those changes were made on a public Github repository, not on this blog.
As this series has proved to be popular, I've decided a few months ago to move it to the Symfony documentation itself where it would be more exposed and maintained by the great Symfony doc team. It was a long process, but it's done now.
Enjoy the new version in a dedicated documentation section, "Create your PHP Framework", on symfony.com.