1 cup butter, room temperature (I soften mine in the microwave at 10% power for 90 seconds at a time until bendable, usually 3 times if it's straight from the fridge)
1 cup dark brown sugar
1/2 c sugar
1 Tbsp vanilla
2 eggs, room temperature (you can put these in a bowl of warm water if you're in a rush)
2 1/2 c AP flour
1 tsp salt
1 tsp baking soda
2 c chocolate chunks
Cream butter on high until white (3-4 minutes). Add sugars and cream until light and fluffy (usually another 4 minutes in my KitchenAid mixer). Really beat it to death, I realized as late as a couple of years ago that I was not actually waiting until the sugar and butter was creamed. Here's a good picture of how it might look (though yours will be darker because of the brown sugar). Add in vanilla and eggs (one at a time, beating 1 minute after each addition).
Sift the dry ingredients together and pour into batter. Mix on low (my setting is called stir) just until blended (about 20 seconds). Pour in your chocolate and stir them in by hand until evenly distributed. (You could also add nuts or M&Ms, sometimes I put in coconut and oatmeal along with chocolate chunks).
Scoop cookies with a big ice cream scoop onto a parchment lined cookie sheet. I think the size is essential because you want them chewy on the outsides and gooey on the insides. Now here is the secret: refrigerate or freeze the cookie dough balls for at least 12 hours (preferably 48 hours). Supposedly this helps the eggs get absorbed by the dry ingredients.
Bake the cookies in a preheated 325 oven for 12-14 minutes, rotating cookie sheet halfway through. Take them out just as they are set and leave them on the hot sheet to finish cooking.