Pour the heavy cream and whole milk into a saucepan and place over med-high heat. 
When the milk begins to steam, whisk the milk as you add the unsweetened cocoa, gingerbread syrup, dark brown sugar, and pure vanilla extract.
Continue to stir until the ingredients are thoroughly mixed. Taste and adjust the flavor to your liking. 
Pour the hot cocoa into serving mugs, add marshmallows, drizzle with chocolate syrup, and dust with gingerbread powder.
Serve.