I did grow a chocolate cosmos one year, and even got it to bloom before it expired from the relentless heat here. The flowers are lovely and absolutely do smell like chocolate.
Recommend you buy a plant already started, rather than trying to start it from seed. The company I got mine from didn't sell them this year, but I've seen them available online. Here it is at Burpee's but they only ship it in the spring, it seems
http://www.burpee.com/flowers/...