Preheat your oven to 350°F. Prepare baking sheets with parchment paper or silicone mats.
Sift the flour, cocoa powder, baking powder, and salt together in a medium bowl. Set aside.
Combine butter, dark brown sugar, and granulated sugar in a mixer. Whip until smooth. Add egg, egg yolk, and vanilla, mixing until blended. Gradually mix in the flour mixture, then fold in chocolate chips.
Place 1 1/2 tablespoon rounds of dough on the prepared sheets using a cookie scoop.
Bake for 12-15 minutes until firm. Cool on baking sheets for 10 minutes before transferring to wire racks.
For topping, mix evaporated milk, sugar, egg yolk, and butter in a saucepan over medium heat. Stir until thickened (10 minutes). Remove from heat and mix in vanilla, coconut, and pecans. Cool before spreading on cookies.
Drizzle melted chocolate over cooled cookies. Let rest for 15 minutes before serving.