Over the years I've messed with the recipe, reducing the butter and switching to dark chocolate chips. (Feel free to substitute semi-sweet if you prefer.) Since I moved back to the intermountain west I've made changes to both ingredients and cooking temperature to deal with high altitude baking problems. I also started making them with partial white whole wheat flour, which adds a pleasant nuttiness to the flavor but can make them dry, so I added an egg yolk. Now they're just about perfect, though there are still a couple of tweaks I want to try!
If you don't want to mess with the whole wheat flour, use all purpose and leave out the extra egg yolk.
High Altitude Chocolate Chip Cookies
3/4 c salted butter, at room temperature (1 1/2 sticks)
139 g sugar
150 g brown sugar
1 1/2 teas vanilla
2 eggs plus 1 egg yolk
200 g white whole wheat flour
129 g all purpose flour
1 teas salt
1 teas baking soda
1 c chopped walnuts
2 c dark chocolate chips (Guittard are my favorite)
(If you don't have a kitchen scale, use the following amounts. Though not as precise, the cookies will still have better texture and flavor than the original sea level recipe. For each sugar, use: 1/2 cups + 3 generous tablespoons. For flour, use a combined amount of 2 1/4 c + 2 generous tablespoons.)
Preheat oven to 350F. If you haven't thought ahead, remove butter from the fridge, cut it up into tablespoons, and set out on a plate. It will be close enough to room temperature in about 10 minutes, while you are getting out the mixer and gathering all the other ingredients.
Beat butter, sugars, and vanilla in a stand mixer until creamy. I look for the color to lighten significantly, and scrape down the bowl several times. Add eggs and yolk, then mix again. Add flour, baking soda, and salt, then mix again. Finally, add the chocolate chips and nuts, and mix in.
Drop roughly tablespoon-sized portions of dough onto ungreased cookie sheets, then bake for about 12 minutes until the cookies are beginning to brown on the edges. Let the cookies rest on the cookie sheets for a couple of minutes before moving them to cooling racks.