Combine Rice Krispies cereal, butter and sugar in a medium bowl. Set aside 1/3 of mixture for topping.
With back of spoon press remaining mixture evenly and firmly into the bottom of an 8×8 pan or a pie plate. Chill.
In a large bowl, fold gently the sweetened condensed milk and whipped topping until combined, being careful to keep the mixture light and fluffy.
Add the lemonade concentrate and continue to gently fold. Be sure to avoid letting the mixture get too liquid-y.
Pour over Rice Krispie crust. Sprinkle reserved crumbs over the top of the lemonade layer. Chill until firm at least 9-10 hours or overnight.