And then there’s The Food Lab: The Science of the Best Chocolate Chip Cookies
http://sweets.seriouseats.com/2013/12/the-food-lab-the-best-chocolate-chip-cookies.html

The long and shortening of it:

Butter: keeps cookies tender because it inhibits the formation of gluten (flour + water from the eggs). The more butter, the more tender the cookie, and the more it spreads as it bakes.
Ideal ratio: 1 part butter to 1 part sugar to .8 part flour
Don’t go for shortening
Melted butter = denser cookies, whereas creamed butter = cakier cookies

Eggs: “By keeping the total mass of egg added to a dough the same but altering the proportion of white to yolk, you can achieve a variety of textures. Two whites and a yolk, for instance, produces the more open structure of the top cookie in the photo above, while three yolks and no whites produces the denser, fudgier texture of the cookie on the bottom.”
Extra egg whites = taller cookies; extra egg yolks = fudgier cookies
Ideal ratio: 1 yolk to 1 white (oh, they way eggs come naturally)

Sugar: Blend only the white sugar with the eggs to give a jump start on caramelization then add brown sugar later with the melted butter.

Chocolate: Hand-chopped chocolate = most intense flavour and interesting texture.

“Here’s what we’re working with so far: White sugar is beaten into whole eggs until it dissolves. Butter is browned and chilled with an ice cube to add back lost moisture and hasten its cooling, before being beaten into the egg mixture, along with brown sugar and. Flour and baking soda are folded in very gently, along with chocolate.”

Salt & Vanilla: Salt is essential to balance the flavour of caramelized sugars, and a good amount of vanilla is a must. Press coarse salt to the cookie tops when they first come out of the oven.

Cooler oven = wide cookies, hotter oven = compact cookies That said, caramelization occurs at 356 degrees so if your recipe calls for the oven to be set at 350 degrees, you’re out of luck. Crank up the heat.

Let the dough rest overnight for superior flavour