Step 1: In a small, microwave-safe bowl, combine the unsweetened cocoa powder, granulated sugar, and salt. Whisk them together to remove any clumps.
Step 2: Add the hot water to the cocoa mixture. Whisk vigorously until the cocoa and sugar are fully dissolved, creating a smooth, thick chocolate syrup. Allow this mixture to cool slightly.
Step 3: Once the syrup has cooled, add the chopped dark or semi-sweet chocolate to it. Gently heat this mixture in the microwave for 15-30 seconds, stirring until the chocolate is fully melted and incorporated, creating a rich chocolate base.
Step 4: Pour the chocolate base into your blender. Add the milk, vanilla extract, and ice cubes.
Step 5: Blend on high speed until the mixture is completely smooth and thick, with no visible ice chunks. This might take 1-2 minutes, depending on your blender. Adjust thickness by adding more milk (if too thick) or more ice (if too thin).
Step 6: Immediately pour your perfectly blended frozen hot chocolate into chilled glasses.
Step 7: Top with a generous swirl of whipped cream, a dusting of extra cocoa powder, and perhaps some chocolate shavings or mini marshmallows for garnish. Serve immediately and enjoy!