Preparation

• Line two large rimmed baking sheets with parchment, and tape the parchment to the baking sheets. Put a piece of parchment on the counter, too. Have ready an instant-read thermometer. Have your toppings ready, too.

Melt and temper the chocolate

• Finely chop 2 lb. of the chocolate and put it in a heatproof bowl that fits snugly over a 4-quart saucepan. Cut the other 1 lb. of chocolate into two pieces.
• Fill the saucepan with about 2 inches of water (it should not touch the bowl). Bring the water to a boil, remove the pot from the heat, and put the bowl of chocolate over it. Gently stir the chocolate occasionally with a silicone spatula until it is fully melted and reaches between 115°F and 120°F on an instant-read thermometer, 10 to 12 minutes.
• Remove the bowl from the pot, wipe the bottom dry, and add one of the 1/2 lb. blocks of chocolate to the bowl. Constantly fold the solid chocolate with the melted chocolate; the solid chocolate will melt somewhat but not fully. Take the temperature of the chocolate now and then. When it drops to 95°F, after 4 to 5 minutes, take what’s left of the solid chocolate out of the bowl. Add the second block of chocolate and fold constantly. When the temperature drops to 90°F, take the block out. (The chocolate blocks can be reused for other recipes.) Gently stir the melted chocolate for 1 minute more.

Spread the chocolate, top, and cool

• Divide the melted chocolate between the prepared baking sheets, and working quickly, spread it to about 1/4 inch thick with an offset spatula. Immediately sprinkle the mango and coconut flakes over both sheets of warm chocolate, pressing down lightly, and then sprinkle each sheet with the chile powder.
• Place in a cool (60°F to 65°F) room or refrigerate it for just 5 minutes to set. For best results, let the bark sit for 12 hours before breaking it into shards.