In a small bowl, stir together the sugar and cocoa powder and set aside.
In a 1-quart saucepan, melt butter over medium heat. Whisk in milk. Add cocoa and sugar mixture and whisk until smooth. Continue to whisk continuously, until mixture begins to bubble.
Remove from heat and stir in vanilla (if desired). Allow to sit and thicken while you make your frozen hot chocolate.
Frozen Hot Chocolate
In a small bowl, stir together sugar and cocoa powder, making sure to mix well and crush any cocoa powder lumps.
In a 16-ounce mason jar or large, microwave-safe mug, microwave water for 30 seconds to 1 minute, until steaming. Stir in cocoa powder and sugar mixture until smooth. Stir in 1 cup of the milk.
Combine ice, cocoa and milk mixture, and remaining 1 cup of milk in your blender and blend on high until smooth.
Divide frozen hot chocolate between glasses, top with optional whipped cream and chocolate syrup. Serve and enjoy!
Notes
Approximate nutritional information is for three servings and was calculated using 2% milk. Does not include whipped cream.*Add an extra heaping tablespoon or two of sugar if you prefer your frosty drinks on the sweeter side.*If using an underpowered blender, use crushed ice if possible as it will be easier for your blender to process.