Preheat and prepare cookie sheets. Position a rack in the center of the oven. Preheat the oven to 375°F (190°C). Line a cookie sheet with parchment paper (or a silicone baking mat). You can bake these cookies right away or chill the cookie dough overnight (for softer, chewier cookies that spread less I like to chill them but they can be baked right away).
Toast pecans. On a large baking sheet, spread pecan halves out. Bake in the preheated oven for 7-8 minutes until fragrant and browned. Remove from the oven and allow to cool. Chop finely and set aside.
Brown the butter. In a medium saucepan, melt the butter over medium heat, then bring it to a boil. Once it starts boiling, swirl the pan constantly until the butter passes foamy phase and becomes a deep amber color. Remove from the heat, and allow the butter to cool slightly. Combine dry ingredients. Whisk together flour, baking soda, baking powder and salt in small bowl.
Combine butter and wet ingredients. In a large mixing bowl, whisk together the browned butter, granulated sugar, brown sugar, eggs, and vanilla until evenly mixed.
Add dry ingredients. Gradually beat in flour mixture. Do not overmix at this point or the cookies will come out tough. Stir in chocolate chips and pecans.
Scoop the cookies. Using a 1-inch cookie scoop or a tablespoon, scoop the cookies into 1 ½ inch balls onto prepared cookie sheets about 2 inches apart.
Bake and cool cookies. Bake the cookie sheet on the middle rack for 10-12 minutes, until lightly browned on the sides. The centers will still look soft. Remove from the oven and let cool on a baking sheet for 5 minutes before transferring to a wire rack to cool completely.