Laravel Notification is unable to send HTML email, why?

I'm using Laravel Notifications and trying to send an email via the toMail method. There is no real logic in my notification.

Below is the class.

<?php

namespace App\Notifications;

use Illuminate\Bus\Queueable;
use Illuminate\Notifications\Notification;
use Illuminate\Contracts\Queue\ShouldQueue;
use Illuminate\Notifications\Messages\MailMessage;
use App\Models\EmailContentModel;
use App\Traits\NotificationContentOverrides;

class EmailVerification extends Notification
{
    use Queueable;
    use NotificationContentOverrides;

    private $url;

    /**
     * Create a new notification instance.
     *
     * @return void
     */
    public function __construct(String $url)
    {
        $this->url = $url;
    }

    /**
     * Get the notification's delivery channels.
     *
     * @param  mixed  $notifiable
     * @return array
     */
    public function via($notifiable)
    {
        return ['mail'];
    }

    /**
     * Get the mail representation of the notification.
     *
     * @param  mixed  $notifiable
     * @return \Illuminate\Notifications\Messages\MailMessage
     */
    public function toMail($notifiable)
    {
        return (new MailMessage)->view('emails.dynamic');
    }

    /**
     * Get the array representation of the notification.
     *
     * @param  mixed  $notifiable
     * @return array
     */
    public function toArray($notifiable)
    {
        return [
            //
        ];
    }
}

This errors with:

Trying to get property 'view' of non-object

Coming from:

/vendor/laravel/framework/src/Illuminate/Notifications/Channels/MailChannel.php:92

According to the docs I should be able to do what I'm doing, which is returning a MailMessage with a view.

My view is very simple. It's just a file that contains a string of Hello for testing purposes.

Things I've ruled out:

dd((new MailMessage)->view('emails.dynamic')->render()); outputs the expected string so it isn't a problem with the view or path.

$notifiable is a user model. I can see an email attribute in there. It's all correct.

I've changed my email settings to log to rule that out.

Looking at vendor/laravel/framework/src/Illuminate/Notifications/Channels/MailChannel.php I'm not sure if this whole thing is expecting some markdown. I don't want to use markdown, I want to use a HTML email/view. Is this the case?

I can create a Mailable class for each of my notifications (php artisan make:mail) but I'm unsure if that's required? According to the docs it isn't.