I like to ask them "Who designed the designer?" Suddenly something extraordinarily complex doesn't need to be designed. It's the old turtle standing on a turtle theory -- a child-like conceptual ability. And they're so cute when they're asleep.
That question is not a difficult one. So I'll assume you are asking it. Short answer:
If God created time and the universe, He must have existed outside of time and the universe. Although everything in the universe must have a cause/beginning, God is the Causer and Sustainer of the universe and therefore the Uncaused Cause.