Melt butter in a large pot on medium-low heat

Add the marshmallows and allow the mixture to melt and become smooth, stirring continuously with a wooden spoon

Remove the pan from the heat and add peanut butter and powdered milk; stir until well blended

Fold in the cheerios until they are well coated with the marshmallow mixture

Press the cheerio treat mixture into a grease 8x8 inch square glass pan

Allow the mixture to cool slightly and then cut into squares store in an airtight container