Custom Field Automation Issues

Hi all!

I do internal communications through constant contact. I am making automated email that sends on employee anniversaries. Using the default anniversary date field in the body of the email displays the date as: "YYYY-MM-DD," which is less than ideal. So, I figured I'd create a custom text field where I could spell out, "Month DD, YYYY," but whenever I use the custom text field I just get: "[[custom.anniversary_date OR ""]]." in the preview and in the test email. What am I doing wrong here? What's the best way to do a custom date spelled out, "Month DD, YYYY"?