Returns the recipe instance for the given badge slug.
        If badge has not been registered, raises ``exceptions.BadgeNotFound``.

def get_recipe_instance(self, badge):
        """
        Returns the recipe instance for the given badge slug.
        If badge has not been registered, raises ``exceptions.BadgeNotFound``.
        """
        from .exceptions import BadgeNotFound
        if badge in self._registry:
            return self.recipes[badge]
        raise BadgeNotFound()