To the crock pot, combine whole milk, vanilla extract, white sugar, heavy cream, cinnamon, nutmeg, and chili powder with a whisk until well-mixed.
Add chocolate chunks to the milk mixture. They will sink to the bottom and that is ok.
Set your crockpot on low and cook for 3 hours, covered, making sure to stir with your whisk every 30 minutes. When stirring, make sure your whisk is reaching the bottom of the crock pot where the chocolate is sitting.
Once completely heated, the hot chocolate should be creamy and warm. Top with marshmallows and serve warm with a sprinkle of cinnamon.
Notes
This crockpot Mexican Hot Chocolate should be stored in your refrigerator covered for up to 3 days. It can also be frozen in a freezer-safe airtight container for up to 3 months.
You can also make this Mexican hot chocolate in a large pot on your stovetop. Heat the combined ingredients over medium heat, stirring constantly, until creamy and hot.