How can I go from a small niche to a larger niche?

Last year, I wrote a book and started selling it online. It's had a little success, but I'm starting to realize that I can target a larger segment of this niche.


The problem is, everything, from my domain, to my e-mail list, to the little bit of branding that I've done, is focused on the small micro-niche.


Let's say that my book is about baking the best chocolate chip cookies (that's not really that subject). So I registered bestchocolatechipcookies.com and built my website there. Most of my backlinks are some variation of "best chocolate chip cookies".


Now I want to move up in my niche and change my focus to the best recipes of any type, and get the domain bestrecipes.com (again, this is just an example).


I'm not really asking about the technical aspects. What I'm concerned about is how I can smoothly change the business so the new, larger site gets the traffic and associated goodwill from the visitors to my current site?


Should I move the content from the small site to the larger one and do re-directs? Or should I leave everything where it is and just put a little graphic on the small site saying, "Now part of the BestRecipes.com family!"


Has anyone done this? If so, what worked (or didn't work)?

Thanks!