Preheat oven to 350ºF. Line baking sheets with parchment. In a small bowl, stir flour with cocoa, baking powder and salt.
In a large bowl, beat butter with 1/2 cup icing sugar until creamy, about 2 minutes. Beat in egg and vanilla until mixed. Gradually beat in flour mixture until evenly mixed. Stir in chocolate chips and pecans.
Take teaspoonful and roll into ball. Place on baking sheet. Continue with remaining dough, placing 2 inches apart. Bake in preheated oven, turning halfway through baking, until cookies are set, about 10 to 14 minutes.
Remove cookies to a cooling rack. When cool, refrigerate cookies up to 1 week or freeze for 1 month. Just before serving, roll cookies in icing sugar to evenly coat.