Pour a milk in a deep pan on a medium heat.Add sugar or sugar powder in it. Simmer it for a while

Make a slurry. Add milk,cocoa powder and corn flour in a separate bowl and mix it well.set aside.

Now add this mixture into pan. Add dark chocolate into this and Stir it continuously. Heat for a while (4-5 minutes). Off the heat.Serve crushed ice into glass and pour cocoa.Mix it well and serve chilled cocoa