Gather the ingredients.
Combine sugar, cocoa powder, and salt in a saucepan; add boiling water and whisk until smooth. Bring mixture to a simmer, stirring continuously to prevent scorching, and cook until slightly thickened, about 2 minutes.
Stir in milk and heat until very hot without boiling.
Remove from heat; add vanilla.
Add cream to each mug to help cool cocoa to drinking temperature, then divide hot cocoa between 4 mugs.
Serve hot and enjoy!
