Why did my chocolate chip cookies become so and crispy, and also a few other questions?

TL;DR: 1. Did my cookies become so dry and crispy because I replaced the light brown sugar with dark brown sugar? and 2. Can I improve the dry-looking texture by adding one more egg? Today I decided to make some chocolate chip cookies with a different recipe from what I usually do. This is the new recipe I used today: https://sugarspunrun.com/worst-chocolate-chip-cookies/. Right after taking them out of the oven and letting them harden for ~5 minutes, they were perfectly soft like they should be. After about ~30 minutes, they were actually hard and crisp. I did some googling and I may have an idea what caused it. The store had run out of vanilla extract and cornstarch, so I completely left out the vanilla extract and replaced the 2 teaspoons of cornstarch with 4 teaspoons of all-purpose flour, but I don't think that is the reason why they came out hard. The ingredients said light brown sugar, however, I didn't have that at home so I used dark brown sugar instead. I think this is the reason why they came out so hard. Is this correct? Here is a picture of them right out the oven: Cookies right out the oven (they look better in this photo, the real color wasn't this saturated) Cookies after chilling for ~5mins They have a very dry texture (also tasted kind of dry), could this be improved by adding one more egg for the moisture? Also, just out of interest, is there something else I could do to improve these? submitted by /u/Eldemarkki [link] [comments]