100 g unsalted butter
1 pack Marie biscuit
1 can condensed milk
2 tbsp cocoa powder

Crush the biscuits. Add cocoa powder, butter and condensed milk.
Mix well until it turns into a paste.
Take an aluminum foil and put the mixture into it.
Roll it and keep in the refrigerated for 5 hours.
Cut with the foil paper like cutting swiss roll.
Serve chilled.