Preheat oven to 350 degrees and grease a 13X9 cake pan.
Whisk cake mix, buttermilk, melted chocolate, eggs, salt, and vegetable oil in a mixing bowl. Pour in prepared cake pan and bake for 30 minutes.
When cake has baked poke all over with a wooden skewer. Let cool. Whisk three milks together. Pour over cake. Combine whipped topping and coconut extract. Spread evenly over cake. Sprinkle with shredded coconut. Cover with plastic wrap and let set in the fridge for two hours before serving. Store in fridge.
Recipe by Cooking for Keeps at https://www.cookingforkeeps.com/chocolate-coconut-tres-leche-cake-lightened-up/