Preheat the oven to 340°F (170°C) and line an 8 inch square baking pan with parchment paper. Set aside
In a small bowl, combine the flour, salt, baking powder, and pumpkin pie spice. Set aside.
In a large bowl, stir together the melted butter, sugar, egg, egg yolk, pumpkin purée and vanilla. Add the dry ingredients along with the pecans and chocolate chips, and stir until just combined.
Pour the batter into the prepared pan, top with additional chocolate chips and pecans, and bake for 25-28 minutes, or until a toothpick inserted into the center comes out clean or with a couple crumbs on it. Let it cool completely before cutting and serving.