// Menu model
public function products(){
    return $this->belongsToMany('Product');
}

public static function getMenuWithProducts($month, $year){
    return self::
        where('month', '=', $month)
        ->where('year', '=', $year)
        ->with('products')
        ->get();
}

public static function getMenuWithProducts($month, $year){
    return self::
        where('month', '=', $month)
        ->where('year', '=', $year)
        ->with('products')
        ->with('producer')
        ->get();
}

BadMethodCallException
Call to undefined method IlluminateDatabaseQueryBuilder::producer()

public function products(){
    return $this->belongsToMany('Product');
}

public function producer()
{
    return $this->belongsTo('Producer');
}