Preheat oven to 375°F. Line baking sheets with parchment paper or lightly grease them; set aside.
Place ½ cup butter in a microwave-safe bowl and microwave on HIGH 40–45 seconds, or until melted. Stir until smooth.
Add ½ cup packed brown sugar and ½ cup sugar to the melted butter and stir until combined.
Add 1 egg (lightly beaten) and 1½ tsp vanilla; mix until smooth.
Add 1½ cups all-purpose flour and stir until just combined, scraping the bowl as needed. Do not overmix.
Fold in 1½ cups chopped pecans until evenly distributed.
Using a small cookie scoop or a tablespoon, drop rounded portions of dough about 2 inches apart onto the prepared baking sheets.
Bake on the center oven rack 8–10 minutes, until the edges are slightly brown.
Cool the cookies on the baking sheet 2 minutes, then transfer to a wire rack to cool completely.
When cookies are cool, sprinkle with powdered sugar to taste.