When I make this recipe, I like it to be so hot it's barely edible, so I put in about a dozen serano peppers. If you want it milder you can just add one or two jalapenos or omit them entirely. I also put canned jalapenos in mine which I don't think are very spicy but they do add a nice peppery flavor. I like to serve this chili in sour dough bread bowls. Note: When I do anything in the slow-cooker, I always wait and add the onions a couple of hours before the end. When you leave onions in a slow-cooker too long they get an upleasant taste which taints the whole dish. This is just a preference of mine; if they don't bother you you can put them in with the rest of the ingredients.