1. Preheat the oven to 350°F (175°C) and grease a 9×13-inch baking pan.

2. In a large bowl, beat together the chocolate cake mix, eggs, vegetable oil, buttermilk, and vanilla extract until smooth. Pour into the prepared pan and spread evenly.

3. Bake for 28–32 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs. Let the cake cool in the pan for about 10 minutes.

4. While the cake cools slightly, combine the sweetened condensed milk, shredded coconut, heavy cream, vanilla, and a pinch of salt in a saucepan over medium-low heat. Stir often for 4–5 minutes until warmed through and slightly thickened.

5. Using the handle of a wooden spoon, poke holes all over the warm cake, spacing them about an inch apart.

6. Slowly pour the warm coconut filling over the cake, letting it soak down into the holes.

7. In a small saucepan, heat the heavy cream just until steaming. Pour it over the chocolate chips in a heatproof bowl and let sit for a minute, then whisk until smooth. Stir in the butter and a pinch of salt until fully melted.

8. Let the chocolate topping cool for 5–10 minutes so it thickens slightly but is still pourable.

9. Pour the chocolate topping evenly over the coconut-soaked cake and spread gently to the edges. Sprinkle with extra shredded coconut if desired.

10. Refrigerate for at least 2 hours, or until the topping has set and the filling has firmed up.

11. Slice and serve chilled or at room temperature.