This system matches what the Blade system in Laravel, Twigg Template Engine and others.
When you want to reuse portions you would consider the reused portion to be a partial view that doesn't extend anything. It would be called from a view that does extend a layout. This sounds weird at first blush but in the years I've built with the other engines mentioned, it's never been a problem. There is typically more stuff that surrounds the reusable content that is not reusable so it all works out.
Currently, I think there's a bug when trying to insert a view normally within a view so I need to revisit that this week, actually.
Of course - you have the option to continue not using layouts, also.