How to recognize when American style chewy cookies are done?

Most cookie recipes (including the Nestle Tollhouse recipe) call for 9 - 11 minutes at 375 ° F (for a 3-bite sized cookie). Within this range, finding the exact time (and temperature) for your preferred done-ness and with your equipment can be a fussy business.

One of the best indicators is the darkening color at the outer edge of the cookie, as shown in the last picture in your recipe. (For what it's worth, substituting dark brown sugar for brown sugar may make a significant difference in the outcome of the cookie.)

You can also gently poke the edge of a cookie to test it. (Only do this if your fingers are used to enough kitchen abuse to be OK with poking hot cookies and gooey melty chocolate.) The edge of the cookie should be a little crispy and have a texture when done. When un-done, it will be liquid and gooey, like the middle of the cookie.

If no other methods prove useful, I fall back to the "test cookie" method, where I bake one cookie at at time at different intervals of time (30 seconds), wait until they cool, and then re-use the time from the best resulting cookie. (Same for dialing the best temperature.) Go with a slightly overdone cookie for a tie breaker; when baking your batches of cookies, the extra mass will take a little longer to bake to the same done-ness. Yes, this is a tedious and fussy procedure, but once you've got this figured out, you can replicate it ever time. And, as with all baking, practice makes perfect.