Using double boiler method. Beat the egg along with cocoa powder, butter and condensed milk.
Whisk until thick and have kind like ribbon stage.
Crush hwa tai marie into 2 or 4 pieces.
In a bowl combine the biscuit and the chocolate mixture.
Toss until all biscuit are well coated with the chocolate.
Pour in a 7 inch baking pan that has been lined with parchment paper.
Press it to make it flat and let it rest in refrigerator until set.