Preheat broiler with rack set fairly close to heat source.

Coat a large, wide heatproof bowl with nonstick spray; place cereal in bowl. Coat a large silicone spatula with nonstick spray as well. Line an 8-inch square pan with plastic wrap and coat with nonstick spray and set all of these aside.

Scatter butter evenly over a rimmed half-sheet pan. Scatter marshmallows evenly all over pan. Place under broiler and watch carefully. In less than 3 minutes the marshmallows should melt, puff up and begin to brown. Use the time cues as a suggestion. You want the marshmallows to be well browned but not burned. Using hot mitts carefully remove pan from oven and tilt it over the bowl of cereal. Use the silicone spatula to scrape butter/marshmallow mixture over the cereal and fold all together until well combined.

Scrape into prepared pan (allow to cool briefly if necessary) and use damp fingers and palms to press down into an even layer. Allow to sit until firm and set, about an hour, or hasten this process by refrigerating briefly (about 15 minutes).

Pull up on plastic wrap and remove the solid square from pan. Set on work surface and peel plastic away and cut into a 5 by 5 grid into 25 bars. These are best served the same day but may be stored in airtight container at room temperature for up to 3 days.

Coat a large silicone spatula with nonstick spray and set aside. Line an 8-inch (20 cm) square pan with plastic wrap and coat with nonstick spray; set aside.

Melt butter in large pot over medium heat. Add marshmallows and melt over medium heat, stirring frequently. When marshmallows are about three-quarters melted add the espresso powder and cinnamon and stir vigorously until marshmallows are completely melted and espresso dissolves. Turn heat off and immediately add cereal to melted marshmallow mixture and use coated spatula to fold together and combine well. Scrape mixture into prepared pan (allow to cool briefly if too hot) and use damp fingers and palms to press down into an even layer. Allow to sit until firm and set, about an hour, or hasten this process by refrigerating briefly (about 15 minutes).

Pull up on plastic wrap and remove from pan. Set on work surface and peel plastic away. Cut into 5 by 5 grid into 25 bars. These are amazing if served the same day but they can be stored in airtight container at room temperature for up to 3 days.