Cooking School: Chewy Chocolate Chip Cookies

This is for Niki. She has been on a quest (part 2 and 3) to find the perfect chocolate chip cookie. I agree with her completely in that personal preferences play a big part in the "perfect" cookie. Of course, ingredients and oven temperatures do, too. I like slightly crisper cookies and I simply love oatmeal in cookies. Niki wants a chewy cookie, the kind you might find at a coffee shop, that retains it's chew even the day after it has been baked. No strange ingredients and no cakiness to be found.
I turned to The Best Recipe for these cookies and, low and behold, they had them! The recipe claimed that the secret was not just in melting the butter, but in the extra egg yolk. Apparently the little bit of extra fat adds just enough moisture to keep the cookies chewy, without making the cookies greasy, as extra butter might.
Just barely cooled and straight out of the oven, these large cookies are perfectly crisp at the edges and chewy - but not cakey - in the center. This may be the perfect way for cookies to be, but all cookies are good fresh from the oven. To test the longer-term claim of chewiness, I left a few out on the counter (out of the reach of my cats) overnight and put the rest into an airtight container. Both groups were still nice and chewy. Success!
I did increase the salt slightly from 1/2 tsp, which I didn't feel was enough. Using salted butter in addition will make them practically irresistable, but unsalted is fine, too. Baking time will vary slightly based on the size of your cookie. The book got 18 cookies from their "scant 1/4 cup" measure. I thought I had just about a full 1/4 cup and still got 24 cookies.

Chewy Chocolate Chip Cookies
(thanks to the Best Recipe)
2 cups plus 2 tbsp ap flour
1/2 tsp baking soda
1 tsp salt
3/4 cup butter (12 tbsp), melted and cooled until just warm
1 cup brown sugar
1/2 cup white sugar
1 egg
1 egg yolk
2 tsp vanilla extract
1 1/4 cups chocolate chips

Preheat oven to 325F. Line a baking sheet with parchment paper.
In a medium bowl, whisk together flour, baking soda and salt.
In a large bowl, whisk together butter and sugars. Beat in the egg, egg yolk and vanilla. Stir in flour mixture, followed by chocolate chips.
Drop by (scant) 1/4 cups onto the baking sheet and pat lightly so the cookie is an even thickness, not a ball shape. Cookies will spread as they bake and this ensures a more even spread.
Bake at 325F for 15-17 minutes, until just turning light brown all over. The edges should only be very slightly more brown, if at all, from the rest of the cookie. Allow cookies to cool before removing them from the baking sheet.
Makes 18-24 large cookies