Warm milk and cream: In a medium heavy-bottomed saucepan, whisk together whole milk, heavy cream, sifted Dutch cocoa powder, sugar (or maple syrup), espresso powder, and a pinch of salt. Heat over medium-low heat until steaming and tiny bubbles form around the edges (do not boil).

Melt chocolate: Remove saucepan from heat. Add the chopped dark chocolate and milk chocolate. Let sit untouched for 1 minute to allow chocolate to soften, then gently whisk continuously until the chocolate is completely melted, glossy, and emulsified into a velvety liquid.

Stir in aromatics: Return saucepan to low heat for 1 minute to ensure it is piping hot. Stir in vanilla extract. Taste and adjust sweetness if desired.

Pour and top: Pour hot chocolate into four heatproof ceramic mugs, leaving 1/2 inch of space at the rim. Arrange 4 large marshmallows tightly across the surface of each mug so they float as a solid blanket.

Torch to golden perfection: Using a handheld culinary kitchen torch on low flame, sweep the flame 2-3 inches above the marshmallows in gentle circular motions until they puff, caramelize, and turn deeply golden-brown with dark blistered edges. (Alternatively, broil on a baking sheet on top rack of oven for 45-60 seconds watching every second).

Garnish and serve: Immediately top with shaved dark chocolate curls and a tiny pinch of cinnamon. Serve hot with spoons to dig through the gooey marshmallow crust!