In a blender, combine the milk, heavy cream, chocolate syrup, powdered sugar, vanilla extract, and ice cubes.
Blend on high speed until the mixture is smooth and frothy, about 30-45 seconds.
Taste the mixture and adjust sweetness if desired by adding more powdered sugar or chocolate syrup.
Pour the frozen hot chocolate into serving glasses.
Top each glass with a generous dollop of whipped cream.
Garnish with chocolate shavings or mini marshmallows for an extra treat.
Serve immediately with a straw or spoon.