Preheat oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper. In a medium bowl, combine flour, cold butter, sugar, and salt until crumbly.

Press the mixture evenly into the bottom of the prepared baking pan. Bake for 10-12 minutes until lightly golden, then set aside.

In a large bowl, whisk together melted butter, brown sugar, eggs, and vanilla extract until smooth.

In a separate bowl, combine flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fold in the chocolate chips and chopped pecans. Spread this filling evenly over the pre-baked crust.

Bake for 20-25 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out with moist crumbs.

Allow the bars to cool completely in the pan before lifting out by the parchment paper and cutting into squares.