Preheat oven to 350°F. Line a 9 x 13-inch baking pan with parchment paper, leaving overhang on the sides for easy removal later. Lightly grease the parchment with cooking spray or butter to prevent sticking.

In a medium saucepan over low heat, combine the unsalted butter with the chopped chocolate. Stir occasionally until completely melted and smooth. Be careful not to overheat. Remove the pan from heat and allow the mixture to cool slightly.

Whisk both granulated sugar and brown sugar into the melted chocolate mixture until well incorporated. Add the eggs one at a time, mixing thoroughly after each addition to ensure a smooth batter. Stir in the vanilla extract until combined.

In a separate bowl, whisk together the flour, sea salt, and cocoa powder. Gently fold this dry mixture into the wet chocolate mixture, stirring just until combined. Avoid overmixing as this can make the brownies tough.

Spread the batter evenly into your prepared pan, smoothing the top with a spatula. Bake in the preheated oven for 22 to 28 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. The center should be just set. Transfer to a wire rack and allow to cool completely.

Combine evaporated milk, egg yolks, granulated sugar, and butter in a saucepan. Cook over medium heat, stirring constantly with a wooden spoon or silicone spatula to prevent scorching. Continue cooking until the mixture thickens to a custard-like consistency, approximately 8 to 12 minutes.

Remove the custard from heat. Stir in the vanilla extract, shredded coconut, and toasted pecans until well combined. Allow the topping to cool slightly, which will help it thicken to a spreadable consistency.

Spread the coconut pecan topping evenly over the cooled brownies. Use an offset spatula to create a smooth, even layer. Refrigerate for at least 45 minutes to allow the topping to set properly before slicing into squares.