1. Preheat the oven to 325°F (165°C).

2. In a saucepan, heat the low-fat milk over medium heat until it simmers.

3. In a mixing bowl, whisk together eggs, butter, coarse sugar, and cocoa powder until well combined.

4. Slowly pour the hot milk into the egg mixture while continuously whisking.

5. Strain the mixture through a sieve to remove any lumps.

6. Pour the custard mixture into ramekins or a baking dish.

7. Place the ramekins or baking dish in a larger pan filled with water to create a water bath.

8. Bake in the preheated oven for about 40-45 minutes until the custard is set.

9. Remove from the oven and let it cool before serving.