In a small bowl, mix together the cocoa powder and warm water to make a paste.
Add the milk, heavy cream, chocolate chips, and cocoa paste to the slow cooker, set to low for one hour.
Stir a few times with a whisk during cooking.
When chocolate is melted, whisk until fully combined and smooth. Add the peppermint extract, vanilla extract, and salt. Taste and add more peppermint extract if needed.
If you want a sweeter, more chocolatey hot chocolate, add ¼ cup more chocolate chips and stir until fully melted.
Serve with whipped cream, crushed peppermint candies, and chocolate shavings to garnish.
Hot cocoa can be kept on the warm setting for several hours, but will need to be whisked a few times as it forms a skin on top.