In a crock pot, combine milk and heavy cream.
Add semi-sweet chocolate chips and cocoa powder to the mixture.
Stir in sugar and vanilla extract until well combined.
Cover the crock pot and set it to low heat.
Cook for 2 hours, stirring occasionally.
Once the chocolate is melted and smooth, adjust sweetness if needed.
Serve hot with whipped cream and mini marshmallows.
Keep the crock pot on warm if serving for a party.
Stir well before serving to mix the ingredients.
Enjoy with friends or family.