01 - In a medium saucepan, combine milk, heavy cream, cocoa powder, sugar, and salt. Heat over medium-low, whisking until just steaming but not boiling.
02 - Add the chopped dark chocolate and whisk until melted and smooth. Remove from heat.
03 - In a separate small saucepan, heat the apple cider until hot but not boiling.
04 - Using an electric mixer or whisk, beat the heavy cream, powdered sugar, ground cinnamon, and vanilla extract together until soft peaks form.
05 - Pour equal parts hot chocolate and hot apple cider into mugs, stirring gently to combine.
06 - Top each mug generously with the cinnamon whipped cream float.
07 - Garnish with a light dusting of ground cinnamon, an apple slice, and a cinnamon stick if desired. Serve immediately.