Heat oven to 350 F and line a 9x13 inch pan with parchment or coat with nonstick spray
whisk melted butter and sugar until glossy then whisk in eggs and vanilla until smooth
fold in cocoa powder then flour baking powder and salt just until combined and stir in chocolate chips if using
spread batter evenly in pan and bake until a toothpick comes out with moist crumbs 22 to 28 minutes then cool in pan on a rack.
Coconut Pecan Topping
In a saucepan over medium heat whisk evaporated milk sugar egg yolks and butter and cook stirring constantly until thickened and lightly bubbling 8 to 12 minutes
remove from heat and stir in vanilla coconut pecans and salt then let stand 5 minutes to thicken slightly
spread topping evenly over cooled brownies and chill or rest until set 30 to 60 minutes then lift out and slice into bars.
Notes
1. Use toasted pecans for deeper flavor. Swap pecans with walnuts or almonds. For less sweetness use unsweetened coconut and reduce sugar by 2 to 3 tbsp. Do not boil topping hard or it can separate. Cool fully before slicing for clean edges