In a small saucepan, heat 1 cup of milk over medium heat until it starts to steam.
In a separate bowl, whisk together cocoa powder, sugar, and salt.
Once the milk is steaming, add the cocoa mixture to the saucepan.
Stir continuously until the cocoa and sugar are fully dissolved.
Add the second cup of milk and continue stirring.
Bring the mixture to a gentle simmer, but do not boil.
Remove from heat and stir in vanilla extract.
Taste and adjust sweetness if necessary.
Pour the hot cocoa into mugs.
Top with whipped cream and sprinkle with chocolate shavings or marshmallows.