Exception in mail queue send function

In my app I am trying to send an email using Mail::queue().

I get an exception saying that serialization of closure failed.

ErrorException in SerializableClosure.php line 93: Serialization of closure failed: Serialization of 'Closure' is not allowed

I have a this as the send function:

public function send()
{
    $view = view('emails.welcome');
    $data = [
        'user' => Auth::user()
    ];

    return $this->mailer->queue($view, $data, function($message){
        $message->to($this->to)->subject($this->subject);
    });
}

I've only recently begun using Laravel so any help would be great.

via Chebli Mohamed