Combine sugar, dry milk and cocoa in bowl; set aside. Heat milk and heavy cream in saucepan on medium heat until simmering. Remove from heat; stir in sugar mixture and 5 oz. TOBLERONE. Use immersion blender to blend until smooth. Scrape side and bottom of pan, then blend another 10 seconds. Transfer to storage container; cool to room temperature. Refrigerate.
For Each Serving: Combine ice, 10 oz. chilled chocolate mixture and 1-1/2 oz. of the remaining TOBLERONE in a blender container. Blend on high speed until smooth; pour into 16-oz. glass. Garnish with whipped cream and remaining 1/2 oz. TOBLERONE. Serve immediately.