To achieve thinner cookies than I’ve done, melt the butter completely before adding it to the sugar mix. Then drop the oven temperature by about 25 degrees Fahrenheit to encourage melting and spreading before the egg proteins firm up. A higher fat European butter has a sharper melting point, and is a sure-fire way to achieve spread.
Another way to go is to use extra large or jumbo eggs, which will introduce more liquid to the equation. Still not enough? Then increase the butter by 50% and melt it. To achieve crispier cookies, increase the proportion of white sugar vis-à-vis brown sugar. Don’t take away the brown sugar completely, since you’re relying on it for that caramelly taste and brown color. However white sugar firms into harder, more candy-like structures, giving the cookie a nice, satisfying crunch.