In a saucepan, whisk together cocoa powder, sugar, and cornstarch until well combined.

Pour in a small amount of milk and stir until a smooth, clump-free paste forms.

Gradually add the rest of the milk while stirring continuously to blend everything smoothly.

Place the saucepan over medium heat and bring the mixture to a gentle simmer, stirring constantly.

Continue to cook until the mixture thickens to a creamy, smooth consistency. The longer you simmer, the denser it becomes. For a classic creamy version, remove from heat once simmering begins.

Pour into mugs and enjoy warm!