Grease and line a 13in x 9in cake tin. 

Melt butter in a pot over low heat. Add marshmallows and stir until melted. Stir in salt and cinnamon powder. Remove the pot from heat and quickly stir in rice krispies and remaining marshmallows until well coated. Use a spatula to evenly press the mixture into the lined tin. Drizzle with milk chocolate and set aside to cool completely. Cut into slices and serve.