Preheat the oven to 350°F (175°C) to ensure even baking.
In a large mixing bowl, beat together the softened butter, brown sugar, and granulated sugar until the mixture is light and fluffy, about 2-3 minutes.
Add the lightly beaten egg and vanilla extract to the butter-sugar mixture and mix until fully incorporated.
In a separate bowl, whisk together the all-purpose flour and chopped toasted pecans. Gradually add this dry mixture to the wet ingredients, stirring until just combined. Be careful not to overmix.
Using a cookie scoop or tablespoon, drop generous portions of dough onto prepared baking sheets, spacing them to allow for spreading.
Bake for 10-12 minutes until edges are lightly golden. Centers may look slightly underbaked but will firm as they cool.
Let cookies cool on baking sheets for a few minutes before transferring to a cooling rack. Once cooled, dust lightly with powdered sugar.