Preheat oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment and lightly grease.

Melt butter and chopped chocolate in a saucepan over low heat, stirring until smooth. Let cool slightly.

Whisk granulated and brown sugars into the chocolate mixture. Add eggs one at a time, whisking well after each. Stir in vanilla.

Whisk flour, salt, and cocoa powder in a separate bowl. Fold into wet mixture until just combined.

Spread batter evenly in pan. Bake 22–28 minutes or until center is just set. Cool completely.

Combine evaporated milk, egg yolks, sugar, and butter in a saucepan. Cook over medium heat, stirring constantly, 8–12 minutes until thick and custard-like.

Remove from heat and stir in vanilla, coconut, and pecans. Let cool slightly.

Spread topping over cooled brownies. Refrigerate at least 45 minutes before slicing.