Heat milk in a saucepan over medium heat.
Reduce heat, add sugar, and stir until dissolved.
Dissolve corn starch in water then add rose water and stir.
Add mixture to milk gradually, stirring till well combined and thickened.
Remove from heat and set aside.
Divide prepared Muhallabeya equally into 2 bowls.
Add Hershey’s chocolate bars to one bowl and Hershey’s cookies and cream to the other.
Mix till well combined and creamy, let cool.
Pour a layer of Hershey’s chocolate Muhallabeya in a serving bowl followed by a layer of Hershey’s cookies and cream Muhallabeya, refrigerate for around 2 hours.
Sprinkle with pistachio and serve.