In a stand mixer, add the dark brown sugar, sugar and butter to the bowl. On medium speed, cream together for about 2 min or until smooth. Scrape down the sides of the bowl about midway through the creaming process. When creaming you are looking for the butter to be lighter in color and soft enough so that you barely feel the grains of sugar if you were to touch it.
Add the egg, vanilla and baking power. Mix until the egg is completely integrated and lighter in color.
While the mixer is on low, add the flour at about a 1/2 cup at a time. Once the dough has come together, which takes about 30 seconds, add the pecans and chocolate chips. Allow the blade to break up the pecans for about 20 seconds.
On a cookie sheet lined with parchment paper ora silpat, scoop out the dough, leaving at least two inches between each cookie. I recommend you do no more than a dozen on a sheet. I use a 1 oz scoop which is equal to 2 tablespoons. Bake in the oven for 14-15 minutes. What you are looking for is light browning on the bottom, with the top just about to brown. Once you are at that point, remove from the oven and let rest for 5 minutes on the cookie sheet. Serve warm or at room temperature. You can also cover and refrigerate the dough and dole out the cookies when you want warm cookies -- simply cook for at least 15 min. Enjoy!