Spicy Hot Chocolate with Chili (Aztec Hot Chocolate)

Name: Spicy Hot Chocolate with Chili (Aztec Hot Chocolate)
Prep time: 2 min
Cook time: 15 min
Total time: 17 min
Cuisine: Mexican
Ingredients: 4 cups whole milk (1 liter); 5 ounces bittersweet chocolate (70% cacao, or semisweet if you like it sweeter, 150 grams); 1 cayenne chilli pepper (roughly chopped); 3 cinnamon sticks (or 1/4 teaspoon ground); 1/2 teaspoon whole cloves (or a pinch ground, optional); 1 teaspoon pure vanilla extract; 1/4-1/2 cup masa harina (4-8 tablespoons, optional, see notes*)