def METHOD_NAME(self) -> jinja2.Environment:
    """Jinja env for this extension."""
    if not current_app.jinja_loader:
        raise ValueError("Expected Flask app to have jinja_loader.")
    ext_loader = jinja2.FileSystemLoader(self.extension_dir / "templates")
    loader = jinja2.ChoiceLoader([ext_loader, current_app.jinja_loader])
    return current_app.METHOD_NAME.overlay(loader=loader)