Step 1

Bring milk and cinnamon to a simmer in a medium saucepan over medium-low heat, whisking occasionally and making sure milk doesn’t boil, until cinnamon is floral and fragrant, about 10 minutes. Whisk in chocolate, sugar, and salt and cook, whisking frequently, until mixture is smooth and creamy and chocolate is melted, about 5 minutes. Pour through a fine-mesh sieve into a large measuring cup; discard cinnamon.

Step 2

Add bourbon to hot chocolate mixture and stir to combine. Divide among mugs, then top with toasted marshmallows.