In a blender, add 500 ml of cold milk, 4 scoops of chocolate ice cream, 2 tablespoons of unsweetened cocoa powder, and 2 tablespoons of sugar. You can adjust the sugar according to your taste preference.
Blend the mixture until it becomes smooth and creamy. If you want a thicker consistency, add more ice cream and blend again.
Pour the chocolate thick shake into tall glasses, leaving some space at the top.
Top each glass with a dollop of whipped cream and garnish with chocolate shavings or chocolate chips.
Serve the chocolate thick shake immediately with a straw and a long spoon.