I have override my skeleton views of the generatorBundle like this post Can't override the standard skeleton views in Symfony2 GeneratorBundle but when i try to add a simple {% extends "AcmeAdminBundle::layout.html.twig" %} or a {% extends "::layout.html.twig" %} in skeleton/crud/views/index.html.twig , I have "[Twig_error_loader] Unable to find template..."
We've extended the default bundle here It might give you some tips.