Preheat oven to 350 degrees.
Line an 8x8 baking pan with parchment and lightly spray with cooking spray.
In a medium bowl combine melted butter, flour and brown sugar together until well combined.
Spread the mixture evenly into pan and press down firmly to form an even layer. Make sure to get in the all the edges and corners.
Bake for 15 minutes.
While crust is cooking prepare filling by mixing together melted butter, brown sugar and corn syrup together until smooth.
Add in egg and vanilla until combined.
Mix in chopped pecans and 1/2 cup chocolate chips.
Once crust has been baking for 15 minutes, remove from oven and pour in filling. Spread out evenly.
Return to the oven and bake for 25-30 minutes. Sides will be bubbling and center will have a slight jiggle.
Immediately sprinkle over remaining chocolate chips and run a butter knife around the edges too loosen up from the sides.
Cool completely before slicing and serving. About 4 hours.