In a medium saucepan, combine peanut butter, granulated sugar, brown sugar, and milk. Cook over medium heat, stirring constantly, until melted and smooth.
Remove from heat and stir in powdered sugar until well combined.
Stir in Rice Krispies cereal until evenly coated.
Press mixture into a greased 8x8 inch baking pan.
Refrigerate for at least 2 hours before cutting into bars.
Notes
Store leftover bars in an airtight container at room temperature for up to 3 days or in the refrigerator for up to a week.