In a sauce pan, mix together unsweetened cocoa powder and powdered sugar. Add 1/4 cup water to it and whisk to get a lump free mix.

Heat the sauce pan over a low to medium flame. Cook for 3-4 minutes while stirring continuously. Turn off the flame when it starts to acquire a syrup-like consistency. Do not over cook the syrup to attain a thick consistency. The sauce thickens further or cooling.

Serve the sauce warm or refrigerate it in an airtight container for up to 10 days.