What is the sentence structure of "lots and lots"

I found the following sentence while I was reading a book which is related to Software Designing. Though I could understand the meaning of the phrase - "lots and lots", I cannot related that to grammar rules. This is mainly attributed to the fact that if I know the grammar and structure of the sentence, I could learn about this more. Therefore, I would be grateful if someone could explain this in terms of grammar.

And it continues with design. Lots and lots of design. Months, maybe years of time spent on design, changing and refining it until it reaches perfection, until it reflects the original vision.