3 of 3 Exemplified domain name according to meta. Fixed Typo

Why is my domain name getting appended to the title in Google SERP?

Suppose my site is example.com.

Now all the results for my site are displayed like this in Google search:

How to make cookies - example.com

However, my title is only How to make cookies, and example.com is not in the title.

This is a custom site, and not a Blogger or WordPress site. I know this happens with Blogger and WordPress blogs since they contain the domain name in their title by default.