1. Combine milk, half-and-half, cinnamon, chiles, zest, and chocolate in a medium pot. Scrape vanilla seeds from pods with side of a knife and add seeds and pods to pan. Bring to a gentle boil over medium-high heat, stirring often; cook 1 to 2 minutes. Remove from heat, cover, and steep about 15 minutes. Strain hot chocolate into a bowl, then return to pot.
2. Heat to steaming over medium heat, stirring. Whirl in a blender in 3 batches until frothy and pour into a pitcher or mugs. Garnish with shaved chocolate if you like.
Make ahead: Through step 1 up to 3 days, chilled.
Note: Nutritional analysis is per serving.