Okay now this is my first tutorial, so if there's any vagueness, please just ask and I'll do my best to clarify. My camera's batteries were dying so I tried to get the pics quickly, and some of them came out a little blurry =( I think, though, that they are clear enough to get the point across.
Step 1: Get your mise en place. In this case, you'll need some baked cookie colored clay (a golden tannish color), some semisweet chocolate color (a rich brown mixed with a hint of black), and some kind of a pin. I make my own out of wire and give it a sort of corkscrew, so that it stays in well. http://i68.photobucket.com/albums/i33/Nibiruflux/cookietut1.jpg
Step 2: Make the cookie shape (a domed disc), imbed the pin, make the chocolate chips. Bake the chips first so they don't get all messed up later when you texture the cookie.
Step 3: I use my exacto knife for the next few parts. You could probably use a needle. Anything sharp, really, I suppose. Make a little incision in the clay. This will be a pocket for your chip.
Step 4: When you put the chip in, push it down into the cookie, and bring the cookie clay up around it, like in this picture.
Another picture of a pocket. Try to make them kind of irregular in shape, and randomly placed.
After several chips, you should start to see a fairly realistic cookie emerging from your lump of brown clay. I think what's really key to making it look real, is the little pieces of "dough" that slightly cover the chips. When you bake cookies, you don't start out with a hunk of plain cookie dough, then lay some chocolate chips on top. You don't want your clay cookie to look like that either.
I didn't use 2 of my chocolate chips, but I feel pretty happy with how it looks. I think trying to squeeze in 2 more would have been a bit much.
Step 5: Texturing! this is where your cookie will really get wow factor. As said before, my weapon of choice here is a stiff bristled nylon paintbrush. I've got a veritable arsenal of these. Sorry for the terrible pic, I was struggling to hold my camera with one hand lol. You just want to tap the bristles against the cookie.
So this is what it should look like when you're done using the paintbrush...
Step 6: More texture. Cookies usually have deep pocks and such in the surface. I have a broken toothpick that I use for this part. I wouldn't suggest using anything like a needle with a well defined point. Something jagged and irregular is going to be your best bet. Go at it at different angles, with varying force. If every little irregularity in the cookie is exactly the same shape, they aren't so irregular.
And, uh, bake and yeah that's it =) Hope that helps some.