Because you are not baking this cake, you must heat treat the cake mix to ensure the flour is safe to consume. Pour the dry chocolate cake mix into a microwave-safe bowl. Microwave on high in 30-second intervals, stirring in between, until the mixture reaches 160°F (71°C). This usually takes about 2 minutes. Let the mix cool completely before moving to the next step.

In a large mixing bowl, pour in the cooled, heat-treated chocolate cake mix. Gradually whisk in the full-fat coconut milk. Use a sturdy spatula to fold the liquid into the dry powder until the mixture is smooth, thick, and free of large lumps. The batter will be much thicker than a standard cake batter, resembling a heavy fudge or brownie dough. Fold in half of the shredded coconut.

Line an 8×8-inch square pan with parchment paper, leaving a little overhang on the sides for easy removal. Spread the mixture evenly into the pan, smoothing the top with your spatula. Sprinkle the remaining shredded coconut over the top, pressing it down slightly so it sticks. Cover the pan with plastic wrap and refrigerate for at least 4 hours, or overnight, until firm. Once set, lift the cake out using the parchment paper, slice into squares, and serve cold.