Prep the Pan: Put bag of marshmallows in the freezer and line a 9x9 inch pan with parchment paper. This will make it easier to remove and cut the squares later.

Melt the Chocolate & Butter: In a large microwave-safe bowl or on the stovetop, melt all the chocolate chips, peanut butter, and margarine over low heat. If melting in the microwave, heat in 30 second intervals, mixing in between for a total of 2 minutes or until melted. If using unsalted butter, add a pinch of salt to enhance the flavor.

Mix in Cereal & Marshmallows: Remove the bowl from the heat source and let cool to ensure marshmallows don't melt. Gently fold in the Rice Krispies cereal and frozen marshmallows until evenly coated. Stir the melted chocolate mixture carefully to avoid crushing the cereal.

Press into Pan: Transfer the mixture to the prepared pan. Use a rubber spatula or the back of a spoon to press it down firmly and create an even layer.

Cool and Set: Allow the squares to cool in the refrigerator until the chocolate topping has set, which usually takes about an hour. If you're in a hurry, you can place the pan in the freezer to speed up the process.

Cut and Enjoy: Once the squares are set, remove them from the pan and cut them into your desired size and shape. Then, savor the delicious nostalgia!