I have a script that sends an email using GmailApp with an html body. I would like the html body to include specific values from the Spreadsheet that contains it, but each time the email is sent, the scriptlet I add is displayed as plain text.

email.gs:

```js
function sendEmail() {

  var mailTo = 'example@gmail.com'

  var NAME = SpreadsheetApp.getActiveSheet().getRange('Sheet1!A1').getValue();

  var subject = 'Hello!'
  var html = HtmlService.createHtmlOutputFromFile('body').getContent();

  GmailApp.sendEmail('', subject, '', {

    name: 'Friend',
    htmlBody: html,
    bcc: mailTo

  });

}
```

body.html:

```html
<h1>Good Evening, <? NAME ?> </h1>
<h3>Hello Friend!</h3>
```

"NAME" should be pulled from the specified cell in the sheet whenever the script is run. 

I am guessing that the reason it is displaying as text is GmailApp.sendEmail pastes the raw html into the email and assumes the client will read it, so how could I first get it to process through the script and then paste into the email?