Cartkit & Uniform payment system

You can use the email action with the snippet option:

$form->emailAction([
   'to' => 'me@example.com',
   'from' => 'info@example.com',
   'snippet' => 'order',
   'cart' => $cart,
]);

This uses a site/snippets/order.php snippet to create the email. Inside the snippet you have access to the form $data and to $options['cart'].

To send an HTML email you need a custom email service like this one or use a package like Phpmailer.