Warm the milk in a heat-safe container, like a glass measuring cup, in the microwave for 60-90 seconds. (Or warm in a small pot over medium-low heat on the stove top.)
Vigorously whisk in the cocoa powder, honey, and vanilla.
Top with marshmallows, if using, and serve.
Video
Notes
We usually use whole milk, but any milk will work. (Nonfat milk will not create very creamy results.)
If using nondairy milk, choose an unsweetened nondairy option. Or, if it's vanilla flavor, omit the vanilla extract. If the milk is sweetened, you may not need the additional sweetener.
Cocoa powder tends to have little lumps, so whisk vigorously.
Add a little more cocoa powder and/or sweetener as desired.
I like the Saco or Hershey's special dark brands of cocoa powder.
The marshmallows are optional, of course. We do love the Dandies brand (their peppermint flavor is our fav) and recommend seeing if your store carries them.
Test the temperature of the milk with your finger or take a little sip to ensure it's right for the kids.