A day ahead, divide the pumpkin puree evenly into a 12 muffin pan. Cover with aluminum foil and freeze overnight.
Pour milk into blender and add yogurt. Remove 3 frozen pumpkin puree "muffins" and add to blender. Add brown sugar, hemp seeds, and cinnamon. Puree until blended.
Pour into individual glasses and sprinkle crumbled graham crackers on top. Garnish with a cinnamon stick.