Preheat oven to 350°F. Line an 8x8 inch metal baking pan with parchment paper, leaving overhang on two sides for easy removal. Lightly grease any exposed pan surface.

Combine butter and chocolate in a medium saucepan over low heat. Stir constantly until completely melted and smooth, about 4-5 minutes. Remove from heat and let cool slightly, 5 minutes.

Whisk both sugars into the warm chocolate mixture until well combined. Add eggs one at a time, whisking vigorously after each until fully incorporated. Stir in vanilla. The batter should look glossy and thick.

Add flour, cocoa powder, and salt. Fold with a spatula until just combined and no dry streaks remain. Fold in 3/4 cup shredded coconut, reserving the rest for topping.

Spread batter evenly in prepared pan. Sprinkle remaining 1/4 cup coconut on top, pressing gently to adhere. Bake 32-36 minutes until the top is set with a slight jiggle in the center and a toothpick comes out with moist crumbs. Cool completely in pan on a wire rack, at least 1 hour, before lifting out and cutting into 16 squares.