In a small saucepan combine the chocolate, hot chocolate mix, cocoa powder and ¾ c of the milk. Whisk over medium heat until the chocolate is melted and everything is well combined. Let cool completely. Once cool combine the chocolate mixture with the remaining cup of milk to a blender with 2 cups of ice. Blend well and add more ice if desired. Divide amongst cups. Combine the heavy cream and powdered sugar and whip with a hand mixer until stiff peaks. Top the drinks with the whipped cream and sprinkle chocolate shavings on top. Serve immediately