Drizzle chocolate on insides of two glasses, set aside.
Place espresso, milk, syrup and ice in a large high-speed blender (use more or less syrup to reach desired sweetness). Blend until thick and smooth, adding more ice if needed. Pour into prepared glasses.
Top each s’mores frappe with marshmallows. Optional: Use kitchen torch to roast marshmallow tops. Sprinkle with graham cracker crumbs and drizzle with additional chocolate sauce.