Preheat oven to 375 F. Line baking sheets with parchment paper or silicone baking mat.
In a large microwave-safe mixing bowl, stir brown sugar into melted butter. Let stand 5 minutes.
Add egg and egg yolk; stir to combine.
Stir in vanilla extract.
Add flour, cocoa powder, baking soda, and salt. Stir until just combined.
Stir in coconut, pecans, and chocolate chunks.
Using a medium cookie scoop (1.5 tablespoon), drop scoops of dough 2 inches apart on prepared cookie sheet.
Bake for about 8-12 minutes, or until the edges of the cookies are set.
Let cool on cookie sheet for 5 minutes. Remove to wire rack to finish cooling.
