In the mixing bowl, add butter and both sugars. Beat on low speed until fully combined.
Add the egg and beat again.
Sift flour, baking powder, baking soda, and salt into the butter mixture; you can also sift into a separate mixing bowl.
Using a spatula, mix the batter. Then add chopped pecans and chocolate chips and mix again until all are combined.
Using an ice cream scoop and a digital kitchen scale, if necessary, divide the batter into eight parts. These are chunky cookies, and they need to be big. Do not make the cookies smaller.
Form balls from each part of the batter with your hands.
Place the cookie balls on the baking sheet and cover them with plastic wrap.
Refrigerate the cookie balls for 1-2 hours or overnight. You can also freeze the cookies for a few months in an airtight container.
Bake cookies at 365oF (185oC) in a convection oven for 18-20 minutes. Bake in a regular oven on the "bake" setting at 350oF (175oC) for 15-18 minutes. Do not overbake cookies. Check cookies to see if they are ready by inserting a toothpick in the center, if necessary. Cookies need to be light brown on top.
After baking cookies, remove them to the wire rack and let them cool to room temperature. You can also decorate them with melted chocolate and pecans.
Notes
Use room-temperature butter for easier mixing.
Toast the pecans before adding them to the dough for deeper flavor.
Use chopped chocolate bars instead of chocolate chips for beautiful melted chocolate pools.
Do not skip chilling cookies before baking. This is important for thick cookies.
Slightly underbake the cookies for soft, chewy centers.
For a bakery-style presentation, press extra chocolate chunks and pecans into the cookies immediately after baking.